Apparatuses and methods for continuous production of glass tubing

ABSTRACT

An apparatus for producing composite glass tube with a plurality of glass layers includes a plurality of cylindrical containers of increasing inner dimensions concentrically arranged and stationary. Each cylindrical container includes a side wall, bottom wall, and a delivery ring. Adjacent cylindrical containers define an annular chamber, a flow control region, and an annular flow channel therebetween. The apparatus includes at least one flow control valve positioned in the flow control region and translatable relative to the adjacent cylindrical containers. Translation of the flow control valves relative to the cylindrical containers is operable to change an impedance to flow of molten glass through the flow control region, thereby modifying an overall flow rate or circumferential distribution of molten glass from the cylindrical containers. Systems and methods for producing composite glass tube using the apparatus are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 120 ofU.S. Provisional Application No. 62/592,736 filed Nov. 30, 2017,entitled “Apparatuses and Methods for Continuous Production of GlassTubing,” the entire contents of which are hereby incorporated byreference.

BACKGROUND Field

The present specification generally relates to apparatuses, systems, andmethods for continuously producing glass tubing, in particular glasstubing comprising a plurality of laminated glass layers.

Technical Background

Historically, glass has been used to produce a variety of articles. Forexample, because of its hermeticity, optical clarity, and excellentchemical durability relative to other materials, glass has been apreferred material for pharmaceutical applications, including, withoutlimitation, vials, syringes, ampoules, cartridges, and other glassarticles. Production of these articles from glass starts with providingglass tubing that may subsequently be formed and separated into aplurality of glass articles. Specifically, the glass used inpharmaceutical packaging must have adequate mechanical and chemicaldurability so as to not affect the stability of the pharmaceuticalformulations contained therein. Glasses having suitable chemicaldurability include those glass compositions within the ASTM standard‘Type IA’ and ‘Type IB’ glass compositions which have a proven historyof chemical durability.

Some conventional processes for producing glass tubes are limited to theproduction of glass tubes comprising a single glass composition.Depending on the application, a single composition glass tube may belimited in mechanical strength and/or chemical durability. Mechanicalstrength and durability of glass tubes can be increased throughconventional glass tempering (i.e., strengthening) processes such asion-exchange or thermal tempering. Subsequent strengthening processes,such as but not limited to ion exchange processes, may increase themechanical strength of the single composition glass tubing. However,certain glass compositions are not well suited to ion exchangestrengthening, and strengthening processes like ion exchange may notimprove the chemical durability of the glass tubing. Furthermore, ionexchange strengthening, as well as other tempering processes tostrengthen the glass tubing, may require additional process steps thatincreases the capital, material, and operating costs of producing theglass tubing.

SUMMARY

Accordingly, a need exists for apparatuses, systems, and methods forcontinuously producing glass tube.

According to a first aspect of the present disclosure, an apparatus forproducing glass tubing may include an inner cylindrical containerincluding an inner delivery ring extending from a bottom of the innercylindrical container, the inner delivery ring defining a centralopening in the bottom of the inner cylindrical container. The apparatusmay further include an outer cylindrical container concentricallyarranged to surround the inner cylindrical container. The outercylindrical container may include a side wall and a bottom wallextending radially inward from the side wall to an outer delivery ringextending downward from the bottom wall, the outer delivery ringdefining a central opening in the bottom wall of the outer cylindricalcontainer. The outer cylindrical container may be spaced apart from theinner cylindrical container to define an annular chamber, a flow controlregion downstream of the annular chamber, and an annular flow channelextending from the flow control region to the outer delivery ring. Theapparatus may further include at least one flow control valve disposedwithin the annular chamber and translatable relative to the outercylindrical container. Translation of the at least one flow controlvalve may be operable to change an impedance to flow of a molten glasscomposition through the flow control region. The apparatus may alsoinclude a blow tube disposed within the inner cylindrical container andoperable to deliver a gas flow proximate the inner delivery ring.

A second aspect of the present disclosure may include the first aspect,wherein the at least one flow control valve may comprise a controlelement positioned proximate to the flow control region and a shaftcoupled to the control element and extending upward through the annularchamber.

A third aspect of the present disclosure may include the second aspect,wherein the control element may comprise an outer surface having a shapecomplimentary to a shape of one or both of the side walls or the bottomwalls of the inner cylindrical container or the outer cylindricalcontainer in the flow control region.

A fourth aspect of the present disclosure may include any of the firstthrough third aspects, wherein the at least one flow control valve maybe manually translatable relative to the plurality of cylindricalcontainers.

A fifth aspect of the present disclosure may include any of the firstthrough third aspects, further comprising an actuator coupled to a shaftof the flow control valve, wherein the actuator may be operable totranslate the at least one flow control valve relative to the outercylindrical container or the inner cylindrical container.

A sixth aspect of the present disclosure may include any of the firstthrough fifth aspects, further comprising a plurality of flow gussetsdisposed within the annular flow channel, each of the plurality of flowgussets extending between the inner cylindrical container and the outercylindrical container and from the flow control region to the innerdelivery ring.

A seventh aspect of the present disclosure may include the sixth aspect,wherein the plurality of flow gussets may separate the flow controlregion, the annular flow channel, or both into a plurality of sectors,and the apparatus may comprise a plurality of flow control valves, eachof the flow control valves positioned in one of the plurality ofsectors.

An eighth aspect of the present disclosure may include any of the firstthrough seventh aspects, wherein an axial distance from a bottom of theinner cylindrical container to a distal end of the outer delivery ringmay be greater than an axial distance from a bottom of the innercylindrical container to a distal end of the inner delivery ring.

A ninth aspect of the present disclosure may include any of the firstthrough seventh aspects, wherein an axial distance from a bottom of theinner cylindrical container to a distal end of the outer delivery ringmay be less than an axial distance from a bottom of the innercylindrical container to a distal end of the inner delivery ring.

A tenth aspect of the present disclosure may include any of the firstthrough ninth aspects, wherein the blow tube may include a head disposedwithin the inner cylindrical container, the blow tube may betranslatable relative to the inner cylindrical container, andtranslation of the blow tube relative to the inner cylindrical containermay be operable to modify an impedance to flow of molten glass from theinner cylindrical container to the inner delivery ring.

An eleventh aspect of the present disclosure may include the tenthaspect, wherein the blow tube may be translatable vertically,horizontally, or both relative to the inner cylindrical container.

A twelfth aspect of the present disclosure may include any of the firstthrough ninth aspects, wherein the blow tube may comprise a head, andthe blow tube may extend through the inner delivery ring so that thehead of the blow tube is positioned vertically below the inner deliveryring.

A thirteenth aspect of the present disclosure may include the twelfthaspect, wherein the blow tube may be translatable relative to the innerdelivery ring, and wherein translation of the blow tube may be operableto modify an impedance to flow of molten glass between the head of theblow tube and a distal end of the inner delivery ring.

A fourteenth aspect of the present disclosure may include any of thefirst through ninth aspects, wherein the blow tube may extend throughthe inner delivery ring of the inner cylindrical container, theapparatus may further comprise at least one inner flow control valvedisposed within the inner cylindrical container and translatablerelative to the inner cylindrical container, and wherein translation ofthe inner flow control valve relative to the inner cylindrical containermay change an impedance to flow of molten glass from the innercylindrical container to the inner delivery ring.

A fifteenth aspect of the present disclosure may include the fourteenthaspect, wherein the inner flow control valve may be verticallytranslatable relative to the blow tube.

A sixteenth aspect of the present disclosure may include either of thefourteenth or the fifteenth aspects, wherein the inner flow controlvalve may be horizontally translatable with the blow tube relative tothe inner cylindrical container.

A seventeenth aspect of the present disclosure may include any of thefirst through sixteenth aspects, comprising a plurality of outercylindrical containers of increasing inner dimensions concentricallyarranged in fixed positions about the inner cylindrical container, eachouter cylindrical container having a side wall, a bottom wall extendingradially inward from the side wall, and an outer delivery ring extendingdownward from the bottom wall, wherein each adjacent pair of outercylindrical containers defines an annular chamber, a flow controlregion, and an annular flow channel. The seventeenth aspect of thepresent disclosure may also include a plurality of flow control valves,wherein at least one of the plurality of flow control valves may bepositioned in each annular chamber defined between adjacent pairs ofouter cylindrical containers.

An eighteenth aspect of the present disclosure may include theseventeenth aspect, wherein an outer dimension of each outer deliveryring may increase for each successive one of the outer cylindricalcontainers positioned outward from the inner delivery ring.

A nineteenth aspect of the present disclosure may include either of theseventeenth or eighteenth aspects, wherein an axial distance from thebottom of the inner cylindrical container to the distal end of eachsuccessive delivery ring may increase for each successive delivery ringfrom the inner cylindrical container to an outermost cylindricalcontainer.

A twentieth aspect of the present disclosure may include either of theseventeenth or eighteenth aspects, wherein an axial distance from thebottom of the inner cylindrical container to the distal end of eachsuccessive delivery ring may decrease for each successive delivery ringfrom the inner cylindrical container to an outermost cylindricalcontainer.

According to a twenty-first aspect of the present disclosure, anapparatus for producing glass tubing may include at least onecylindrical container having a side wall and a bottom wall extendingradially inward from the side wall to a delivery ring extending downwardfrom the bottom wall, the delivery ring defining a central opening inthe bottom wall of the cylindrical container. The apparatus may furtherinclude a blow tube disposed within the at least one cylindricalcontainer and operable to deliver a gas flow proximate the deliveryring. The apparatus may further include at least one flow control valvepositioned in a flow control region defined between the cylindricalcontainer and the blow tube and translatable relative to the cylindricalcontainer. Translation of the at least one flow control valve may beoperable to change an impedance to flow of a molten glass compositionthrough the flow control region.

A twenty-second aspect of the present disclosure may include thetwenty-first aspect, wherein the at least one flow control valve may bevertically translatable relative to the blow tube.

A twenty-third aspect of the present disclosure may include either ofthe twenty-first or twenty-second aspects, wherein the at least one flowcontrol valve may be horizontally translatable with the blow tuberelative to the inner cylindrical container.

A twenty-fourth aspect of the present disclosure may include any of thetwenty-first through twenty-third aspects, further comprising an outercylindrical container concentrically arranged to surround the at leastone cylindrical container and spaced apart from the at least onecylindrical container to define an annular chamber therebetween, theouter cylindrical container comprising a side wall and a bottom wallextending radially inward from the side wall to an outer delivery ringextending downward from the bottom wall, the outer delivery ringdefining a central opening in the bottom wall of the outer cylindricalcontainer, wherein the bottom wall, the side wall, or both of the outercylindrical container are spaced apart from the at least one cylindricalcontainer to define a flow control region and an annular flow channelextending between the outer cylindrical container and the at least onecylindrical container and from the flow control region to the outerdelivery ring, and at least one outer flow control valve disposed in theannular chamber and translatable relative to the outer cylindricalcontainer, the at least one cylindrical container, or both, whereintranslation of the at least one flow control valve is operable to changean impedance to flow of a molten glass composition through the flowcontrol region.

According to a twenty-fifth aspect of the present disclosure, a systemfor producing glass tubing may include an apparatus that includes aninner cylindrical container including an inner delivery ring extendingfrom a bottom of the inner cylindrical container, the inner deliveryring defining a central opening in the bottom of the inner cylindricalcontainer. The apparatus may further include an outer cylindricalcontainer concentrically arranged to surround the inner cylindricalcontainer and spaced apart from the inner cylindrical container todefine an annular chamber therebetween. The outer cylindrical containermay include a side wall and a bottom wall extending radially inward fromthe side wall to an outer delivery ring extending downward from thebottom wall. The outer delivery ring may define a central opening in thebottom wall of the outer cylindrical container. The bottom wall, theside wall, or both of the outer cylindrical container may be spacedapart from the inner cylindrical container to define a flow controlregion and an annular flow channel extending between the outercylindrical container and the inner cylindrical container and from theflow control region to the outer delivery ring. The apparatus mayfurther include at least one flow control valve disposed within theannular chamber and at least one positioner operatively coupled to theat least one flow control valve and operable to translate the at leastone flow control valve relative to the outer cylindrical container, theinner cylindrical container, or both. Translation of the at least oneflow control valve by the positioner may be operable to change animpedance to flow of a molten glass composition through the flow controlregion. The apparatus may further include a blow tube disposed withinthe inner cylindrical container and operable to deliver a gas flowproximate the inner delivery ring. The system may further include asensor disposed downstream of the apparatus, the sensor operable tomeasure at least one dimension of the glass tube produced by theapparatus, and a control system communicatively coupled to the at leastone positioner and to the sensor. The control system may include aprocessor and one or more memory modules communicatively coupled to theprocessor.

A twenty-sixth aspect of the present disclosure may include thetwenty-fifth aspect, further comprising machine readable instructionsstored in the one or more memory modules that may cause the system toperform at least the following when executed by the processor: measure adimension of the glass tube, compare the dimension of the glass tube toa target dimension of the glass tube, and send a control signal to theat least one positioner to change a position the at least one flowcontrol valve based on the comparison of the dimension of the glass tubeto the target dimension, wherein changing the position of the at leastone flow control valve produces a change in the dimension of the glasstube.

A twenty-seventh aspect of the present disclosure may include either ofthe twenty-fifth or twenty-sixth aspects, wherein the sensor may beoperable to measure at least one of the overall average thickness of theglass tube, an average thickness of one or more than one glass layer ofthe glass tube, a circumferential thickness profile of the glass tube, acircumferential thickness profile of one or more than one glass layer ofthe glass tube, an outer diameter of the glass tube, an inner diameterof the glass tube, or combinations of these.

A twenty-eighth aspect of the present disclosure may include any of thetwenty-fifth through twenty-seventh aspects, wherein the apparatus mayinclude: a plurality of flow control valves disposed in the annularchamber, and a plurality of positioners, each of the plurality ofpositioners operatively coupled to one of the plurality of flow controlvalves and operable to independently translate the one of the pluralityof flow control valves relative to the outer cylindrical container.

A twenty-ninth aspect may include the twenty-eighth aspect, furthercomprising machine readable instructions stored in the one or morememory modules that may cause the system to perform at least thefollowing when executed by the processor: measure a siding of the glasstube, compare the siding of the glass tube to a target siding of theglass tube, and position at least one of the plurality of flow controlvalves relative to the other of the plurality of flow control valves tochange the siding of the glass tube based on the comparison.

A thirtieth aspect of the present disclosure may include any of thetwenty-fifth through twenty-ninth aspects, further comprising a blowtube positioner operable to position the blow tube relative to the innercylindrical container, wherein the control system may be communicativelycoupled to the blow tube positioner.

A thirty-first aspect of the present disclosure may include thethirtieth aspect, further comprising machine readable instructionsstored in the one or more memory modules that may cause the system toperform at least the following when executed by the processor: measure adimension of the innermost glass layer of the glass tube, compare thedimension of the innermost glass layer of the glass tube to a targetdimension of the innermost glass layer, and position the blow tuberelative to the innermost cylindrical container to change the dimensionof the innermost glass layer of the glass tube based on the comparison.

A thirty-second aspect of the present disclosure may include any of thetwenty-fifth through thirty-first aspects, wherein the dimension may bethe average thickness of the innermost glass layer and the machinereadable instructions stored in the one or more memory modules, whenexecuted by the processor, may cause the system to vertically positionthe blow tube relative to the inner cylindrical container.

According to a thirty-third aspect of the present disclosure, a methodfor producing a glass tube may include introducing a first molten glasscomposition to an annular chamber defined between an inner cylindricalcontainer and an outer cylindrical container. The bottom wall of theouter cylindrical container may be spaced apart from the innercylindrical container to define an annular flow channel. The method mayfurther include passing the first molten glass composition through theannular flow channel to an outer delivery ring coupled to the bottomwall of the outer cylindrical container and defining a central openingin the bottom wall of the outer cylindrical container. The method mayfurther include translating at least one flow control valve disposed inthe annular chamber. Translation of the at least one flow control valverelative to the outer cylindrical container may change an impedance toflow of the molten glass into the annular flow channel, thereby changinga thickness of the glass tube. The method may further include separatingthe first molten glass composition from a distal end of the outerdelivery ring to form a first molten glass layer of the glass tube.

A thirty-fourth aspect of the present disclosure may include thethirty-third aspect, further comprising producing a gas flow proximateto the outer delivery ring.

A thirty-fifth aspect of the present disclosure may include either thethirty-third or thirty-fourth aspect, wherein a plurality of flowcontrol valves may be disposed in the annular chamber defined betweenthe inner cylindrical container and the outer cylindrical container,each of the plurality of flow control valves being independentlytranslatable relative to the outer cylindrical container.

A thirty-sixth aspect of the present disclosure may include thethirty-fifth aspect, further comprising adjusting a siding of the firstmolten glass layer by translating one or more of the plurality of flowcontrol valves relative to the other of the plurality of flow controlvalves to change the circumferential distribution of the first moltenglass composition flowing through the annular flow channel.

A thirty-seventh aspect of the present disclosure may include any of thethirty-third through thirty-sixth aspects, further comprising:introducing a second molten glass composition to the inner cylindricalcontainer, the inner cylindrical container comprising a blow tubedisposed within the inner cylindrical container, passing the secondmolten glass composition through an inner annular flow channel definedbetween the blow tube and the inner cylindrical container to an innerdelivery ring coupled to the inner cylindrical container and defining acentral opening of the inner cylindrical container, and separating thesecond molten glass composition from the inner delivery ring to producea second molten glass layer of the glass tube.

A thirty-eighth aspect of the present disclosure may include thethirty-seventh aspect, further comprising contacting the first moltenglass layer separated from the outer delivery ring with the secondmolten glass layer separated from the inner delivery ring.

A thirty-ninth aspect of the present disclosure may include either ofthe thirty-seventh or thirty-eighth aspects, further comprisingadjusting a thickness or a siding of the second molten glass layer bytranslating the blow tube vertically or horizontally relative to theinner cylindrical container to change an impedance to flow of the secondmolten glass composition between the blow tube and the inner cylindricalcontainer.

A fortieth aspect of the present disclosure may include any of thethirty-seventh through thirty-ninth aspects, wherein the innercylindrical container may include an inner flow control valve disposedwithin the inner cylindrical container and translatable relative to theinner cylindrical container, where the method may further compriseadjusting a thickness or a siding of the second molten glass layer bytranslating the inner flow control valve vertically or horizontallyrelative to the inner cylindrical container to change an impedance toflow of the second molten glass composition from the inner cylindricalcontainer to the inner delivery ring.

A forty-first aspect of the present disclosure may include any of thethirty-seventh through fortieth aspects, wherein the first molten glasscomposition may have a coefficient of thermal expansion (CTE) differentthan the second molten glass composition.

A forty-second aspect of the present disclosure may include any of thethirty-seventh through forty-first aspects, further comprising:introducing a third molten glass composition to a second annular chamberdefined between the outer cylindrical container and a second outercylindrical container; passing the third molten glass composition fromthe second annular chamber, through a second annular flow channeldefined between a bottom wall of the second outer cylindrical containerand the outer cylindrical container, to a second outer delivery ring;and separating the third molten glass composition from the second outerdelivery ring to produce a third molten glass layer of the glass tube.

A forty-third aspect of the present disclosure may include any of thethirty-seventh through forty-second aspects, further comprisingadjusting an average thickness or a circumferential thickness profile ofthe third molten glass layer by translating at least one of a pluralityof flow control valves disposed in the second annular chamber relativeto the second outer cylindrical container.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically depicts a cross-sectional perspective view of anapparatus for producing glass tubing with one or a plurality of glasslayers, according to one or more embodiments shown and described herein;

FIG. 1B schematically depicts a top view of the apparatus of FIG. 1A,according to one or more embodiments shown and described herein;

FIG. 1C schematically depicts a side view in cross-section of theapparatus of FIG. 1A, according to one or more embodiments shown anddescribed herein;

FIG. 2 schematically depicts a side view in cross-section of anotherembodiment of an apparatus for producing composite glass tube with aplurality of glass layers, according to one or more embodiments shownand described herein;

FIG. 3A schematically depicts a perspective view of a flow control valveof the apparatus of FIG. 1A, according to one or more embodiments shownand described herein;

FIG. 3B schematically depicts a side view in cross-section of the flowcontrol valve of FIG. 3A, according to one or more embodiments shown anddescribed herein;

FIG. 3C schematically depicts a top view of the flow control valve ofFIG. 3A, according to one or more embodiments shown and describedherein;

FIG. 4A schematically depicts a side view in cross section of the flowcontrol valve of FIG. 3A positioned at a distance from two cylindricalcontainers of the apparatus of FIG. 1A resulting in a low glass flowrate, according to one or more embodiments shown and described herein;

FIG. 4B schematically depicts a side view in cross section of the flowcontrol valve of FIG. 3A positioned at a medium distance from the twocylindrical containers of the apparatus of FIG. 1A resulting in a mediumglass flow rate, according to one or more embodiments shown anddescribed herein;

FIG. 4C schematically depicts a side view in cross section of the flowcontrol valve of FIG. 3A positioned at a distance from the twocylindrical containers of the apparatus of FIG. 1A resulting in anincreased glass flow rate relative to FIG. 4B, according to one or moreembodiments shown and described herein;

FIG. 5A schematically depicts a side view in cross section of anotherembodiment of an apparatus for producing glass tubing, the apparatushaving a flow control valve positioned relative to the two cylindricalcontainers of the apparatus to produce a large glass flow rate,according to one or more embodiments shown and described herein;

FIG. 5B schematically depicts a side view in cross section of theapparatus of FIG. 5A in which the flow control valve is positionedrelative to the two cylindrical containers of the apparatus to produce alesser glass flow rate compared to FIG. 5A, according to one or moreembodiments shown and described herein;

FIG. 5C schematically depicts a side view in cross section of theapparatus of FIG. 5A in which the flow control valve is positionedrelative to the two cylindrical containers of the apparatus to produce alesser glass flow rate compared to FIG. 5B, according to one or moreembodiments shown and described herein;

FIG. 6A schematically depicts a top view of another embodiment of anapparatus for producing a composite glass tube, the apparatus includingtwo flow control valves, according to one or more embodiments shown anddescribed herein;

FIG. 6B schematically depicts a top view of another embodiment of anapparatus for producing a composite glass tube, the apparatus includingthree flow control valves, according to one or more embodiments shownand described herein;

FIG. 6C schematically depicts a top view of another embodiment of anapparatus for producing a composite glass tube, the apparatus includingsix flow control valves, according to one or more embodiments shown anddescribed herein;

FIG. 6D schematically depicts a top view of another embodiment of anapparatus for producing a composite glass tube, the apparatus havingeight flow control valves, according to one or more embodiments shownand described herein;

FIG. 7A schematically depicts a side view in cross-section of a bottomportion of the apparatus of FIG. 1A, according to one or moreembodiments shown and described herein;

FIG. 7B schematically depicts a side view in cross-section of anotherembodiment of an apparatus for producing composite glass tube with aplurality of layers, according to one or more embodiments shown anddescribed herein;

FIG. 7C schematically depicts a side view in cross-section of anotherembodiment of an apparatus for producing composite glass tube with aplurality of layers, according to one or more embodiments shown anddescribed herein;

FIG. 7D schematically depicts a side view in cross-section of anotherembodiment of an apparatus for producing composite glass tube with aplurality of layers, according to one or more embodiments shown anddescribed herein;

FIG. 8 schematically depicts a perspective view in cross-section of yetanother embodiment of an apparatus for producing composite glass tubewith a plurality of glass layers, according to one or more embodimentsshown and described herein;

FIG. 9A graphically depicts a velocity profile of molten glass through aportion of the apparatus determined using a flow model based on thegeometry of the apparatus of FIG. 1A, according to one or moreembodiments shown and described herein;

FIG. 9B graphically depicts a pressure profile of molten glass through aportion of the apparatus determined using a flow model based on thegeometry of the apparatus of FIG. 1A, according to one or moreembodiments shown and described herein;

FIG. 10 graphically depicts a flow rate of molten glass (y-axis) as afunction of a control element z-position from a minimum operationalopening (x-axis) for the flow model of FIGS. 9A and 9B, according to oneor more embodiments shown and described herein;

FIG. 11 schematically depicts a system for producing a composite glasstube with a plurality of glass layers, the system including theapparatus of FIG. 1A, according to one or more embodiments shown anddescribed herein;

FIG. 12 graphically depicts a 3-dimensional pressure profile for a flowmodel developed for flow of molten glass through a portion of theapparatus of FIG. 1A, according to one or more embodiments shown anddescribed herein;

FIG. 13 graphically depicts a 3-dimensional velocity profile for a flowmodel developed for flow of molten glass through a portion of theapparatus of FIG. 1A, according to one or more embodiments shown anddescribed herein;

FIG. 14 graphically depicts a relative mass flow rate of the moltenglass (y-axis) as a function of a angular position of the glass flow,according to one or more embodiments shown and described herein;

FIG. 15 graphically depicts the 3-dimensional pressure profile for aflow delivery region of the flow model of FIG. 12, according to one ormore embodiments shown and described herein;

FIG. 16 graphically depicts the 3-dimensional velocity profile for aflow delivery region of the flow model of FIG. 13, according to one ormore embodiments shown and described herein;

FIG. 17 graphically depicts a 3-dimensional pressure profile for a flowmodel based on flow of molten glass through an apparatus that includescylindrical containers that are polygonal in cross-sectional shape,according to one or more embodiments shown and described herein;

FIG. 18 graphically depicts a 3-dimensional velocity profile for a flowmodel based on flow of molten glass through an apparatus that includescylindrical containers that are polygonal in cross-sectional shape,according to one or more embodiments shown and described herein;

FIG. 19 schematically depicts a perspective view in cross section of anexperimental apparatus for evaluating operation of the flow controlvalves, according to one or more embodiments shown and described herein;

FIG. 20 graphically depicts fluid velocity (y-axis) as a function ofangular position of the fluid flow (x-axis) for two different positionsof the flow control valves of the apparatus of FIG. 19, where at eachposition, all of the flow control valves are positioned at the samedistance, according to one or more embodiments shown and describedherein;

FIG. 21 graphically depicts fluid velocity (y-axis) as a function ofangular position of the fluid flow (x-axis) for a configuration of theapparatus of FIG. 19 in which one of the flow control valves ispositioned at a different vertical position compared to the other flowcontrol valves to create siding, according to one or more embodimentsshown and described herein;

FIG. 22A is a photographic image of the flow of oil from a delivery ringof the apparatus of FIG. 19 at time equal to zero seconds upon a changeof position of one of the four flow control valves to create siding,according to one or more embodiments shown and described herein;

FIG. 22B is a photographic image of the flow of oil from a delivery ringof the apparatus of FIG. 19 at time equal to 11 seconds after a changeof position of one of the four flow control valves to create siding,according to one or more embodiments shown and described herein;

FIG. 22C is a photographic image of the flow of oil from a delivery ringof the apparatus of FIG. 19 at time equal to 20 seconds after a changeof position of one of the four flow control valves to create siding,according to one or more embodiments shown and described herein;

FIG. 22D is a photographic image of the flow of oil from a delivery ringof the apparatus of FIG. 19 at time equal to 30 seconds after a changeof position of one of the four flow control valves to create siding,according to one or more embodiments shown and described herein; and

FIG. 22E is a photographic image of the flow of oil from a delivery ringof the apparatus of FIG. 19 at time equal to 39 seconds after a changeof position of one of the four flow control valves to create siding,according to one or more embodiments shown and described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of apparatuses,systems, and methods for continuously producing composite glass tube,examples of which are illustrated in the accompanying drawings. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order, nor that specific orientations berequired with any apparatus. Accordingly, where a method claim does notactually recite an order to be followed by its steps, or that anyapparatus claim does not actually recite an order or orientation toindividual components, or it is not otherwise specifically stated in theclaims or description that the steps are to be limited to a specificorder, or that a specific order or orientation to components of anapparatus is not recited, it is in no way intended that an order ororientation be inferred, in any respect. This holds for any possiblenon-express basis for interpretation, including: matters of logic withrespect to arrangement of steps, operational flow, order of components,or orientation of components; plain meaning derived from grammaticalorganization or punctuation, and; the number or type of embodimentsdescribed in the specification.

Directional terms as used herein—for example up, down, right, left,front, back, top, bottom—are made only with reference to the figures asdrawn and the coordinate axis provided therewith and are not intended toimply absolute orientation.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a” component includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

As used herein, the term “siding” refers to the difference between theminimum wall thickness and the maximum wall thickness of a glass tube orthe difference between the minimum layer thickness and maximum layerthickness of a glass layer of a composite glass tube, where the minimumand maximum wall thicknesses or minimum and maximum glass layerthicknesses are determined from a cross-section of the glass tube.

As used herein, “axial” refers the +/−Z direction of the coordinate axisprovided in the figures.

Some glass tube manufacturing processes have been developed to producelaminated glass tubing comprising a plurality of glass layers. In theseprocesses, different glass compositions may be used in each of the glasslayers of the composite tubing to provide different properties to theglass tubing. For example, the glass compositions for the outer glasslayers may be selected to provide additional strength and/or chemicaldurability to the glass tubing. However, these composite glassmanufacturing processes have been restricted to producing laminatedglass tubing with glass layer thicknesses that are generally fixed.Thus, the conventional laminated glass tubing processes are not able toproduce varying thicknesses of each of the glass layers. Additionally,these conventional laminated glass tubing processes do not enablecontrol of the circumferential distribution of glass flow. Thesecomposite glass manufacturing processes may also be limited to batchprocessing of the composite glass tube due to variations in thicknessaround the circumference of the glass tube (i.e., sidings) caused byuneven feeding of the glass compositions to the glass tube formingprocesses.

Embodiments of an apparatus 100 disclosed herein for producing compositeglass tube including a plurality of glass layers are illustrated inFIGS. 1A-1C and FIG. 2. The apparatus 100 may include a plurality ofcylindrical containers 102 of increasing inner dimensions concentricallyarranged and stationary. As used in this disclosure, the term“stationary” as applied to the cylindrical containers refers to each ofthe cylindrical containers 102 being in a fixed position relative toeach of the other cylindrical containers 102. Each cylindrical container102 has a cylindrical side wall 104 (FIG. 2) and a bottom wall 106 (FIG.2) extending radially inward from the side wall 104 to a delivery ring108 (FIG. 2) extending downward from the bottom wall 106. The side walls104 of adjacent cylindrical containers 102 define an annular chambertherebetween. The side walls 104, bottom walls 106, or a combination ofboth of adjacent cylindrical containers 102 may define a flow controlregion in which a distance between the side walls 104 or between thebottom walls 106 decreases. The bottom walls 106 of the adjacentcylindrical containers 102 define an annular flow channel extendinginward from the flow control region to the delivery rings 108 of theadjacent cylindrical containers 102. Molten glass introduced to one ofthe annular chambers may flow downward through the annular chamber,through the flow control region, through the annular flow channel, andto the delivery ring. The molten glass separates from the delivery ring108 to form an annular layer of molten glass that may be combined withother annular layers of molten glass from other cylindrical containers102 to produce the composite glass tube including a plurality of glasslayers. A blow tube 120 may be disposed in the innermost cylindricalcontainer 110 and positioned to deliver a flow of gas to maintain theinner dimension of the composite glass tube.

The apparatus 100 may also include at least one flow control valve 170positioned within the flow control region defined between the adjacentcylindrical containers 102. The flow control valve 170 may betranslatable relative to the adjacent cylindrical containers 102.Translation of the flow control valve 170 relative to the adjacentcylindrical containers 102 may change the impedance to flow of themolten glass through the flow control region, thereby changing the flowrate of the molten glass through the flow control region and the annularflow channel. Changing the flow rate of the molten glass may change thethickness of the annular glass layer associated with the annularchamber. Multiple flow control valves 170 may be independentlypositioned to control the circumferential distribution of glass flowfrom the cylindrical containers, thereby controlling the circumferentialthickness profile of the composite glass tube or a specific glass layer.

The apparatus 100 disclosed herein may enable control of the thicknessof one or a plurality of the glass layers of the composite glass tube orthe ratios of thicknesses between layers of the composite glass tube.Thus, the apparatus may be easily converted between variousconfigurations to produce different composite glass tube products thatinclude different thicknesses and/or different glass compositions. Thismay enable the production of different SKUs of composite glass tubeusing a single apparatus and production line. In addition, the apparatusmay enable control of the circumferential glass flow distribution (i.e.,siding) of specific glass layers, thereby changing the thickness of oneor more portions of the circumference of the composite glass tuberelative to the other portions of the composite glass tube. Thus, theapparatus and method may enable tight control of glass tube dimensions,such as outer diameter, inner diameter, thickness, and sidings, toproduce glass tube that conforms with the tight dimensional tolerancesrequired in certain applications. The circumferential glass flowdistribution may also be adjusted to compensate for circumferentialvariations in the height of the molten glass in each of the annularchambers. Thus, the apparatus may enable each glass composition to becontinuously fed to each annular chamber of the apparatus from a singlefeed tube.

The apparatus may also enable the production of composite glass tubehaving improved chemical durability and mechanical strength by enablingthe use of different glass compositions with different properties foreach of the glass layers of the composite glass tube. Thus, theapparatus may eliminate the need for additional process steps such asion-exchange strengthening, thermal tempering, or other temperingprocesses to strengthen the glass tube post-production. Additionally,some glass compositions may not be suited to ion-exchange strengtheningor other tempering processes. For example, some glass compositions maylack smaller-sized alkali metal ions that are replaced by larger-sizedions during ion-exchange processes. Thus, the apparatus may enable theproduction of strengthened composite glass tube from glass compositionsthat are not suited to ion exchange or thermal tempering.

The embodiment of FIGS. 1A-1C, as well as various other embodiments ofthe apparatuses, systems, and methods for continuously producingcomposite glass tube will be described herein with specific reference tothe appended drawings. Although the apparatuses and systems aredescribed herein in the context of producing a composite glass tubehaving a plurality of layers, it is understood that embodiments of theapparatus may also be adapted to produce glass tube having single glasslayer.

Referring now to FIGS. 1A-1C, as previously discussed, the apparatus 100for producing a composite glass tube with a plurality of layers includesa plurality of cylindrical containers 102 of increasing innerdimensions. Each of the cylindrical containers may be associated withone of the plurality of glass layers. The plurality of cylindricalcontainers 102 may be concentrically arranged and fixed relative to oneanother. For example, the apparatus 100 may include an innermostcylindrical container 110, a first outer cylindrical container 130, anda second outer cylindrical container 150. Although depicted in FIGS.1A-1C as having three cylindrical containers 102, in some embodiments,the apparatus 100 may have more than three cylindrical containers 102,such as 4, 5, 6, 7, 8, or more than 8 cylindrical containers 102. Forexample, FIG. 2 depicts an embodiment of apparatus 100 having 5cylindrical containers 102. In some embodiments, the apparatus 100 mayinclude 2 cylindrical containers 102 or even a single cylindricalcontainer 102. For example, an apparatus having two cylindricalcontainers is depicted in FIG. 19 and is subsequently described in thisdisclosure.

In some embodiments, the cylindrical containers 102, such as theinnermost cylindrical container 110, the first outer cylindricalcontainer 130, and the second outer cylindrical container 150 of FIGS.1A-1C may be constructed of electrically conductive refractory metals.Electrically conductive refractory metals may include platinum orplatinum-containing metals such as platinum-rhodium, platinum-iridium,dispersed hardened platinum materials, and combinations thereof. Forexample, in some embodiments, the cylindrical containers 102 may includeplatinum. In some embodiments, the cylindrical containers 102 mayinclude dispersed hardened platinum. Other refractory metals may includemolybdenum, palladium, rhenium, tantalum, titanium, tungsten, ruthenium,osmium, zirconium, and alloys thereof and/or zirconium dioxide.Alternatively, in other embodiments, the cylindrical containers 102 mayinclude other refractory materials, such as, but not limited to zircon(e.g., zirconia), silicon carbide, xenotime, alumina-based refractoryceramics, aluminosilicate refractory ceramics, other refractorymaterials, or combinations of these. In some embodiments, thecylindrical containers 102 may include a refractory ceramic materialcladded with a refractory metal.

Referring back to FIGS. 1A-1C, the innermost cylindrical container 110has a side wall 112. The side wall 112 may be cylindrical in shape. Asused in this disclosure, the term “cylindrical” refers to an elongatehollow shape and does not imply any specific cross sectional shape. Forexample, when viewed in top view, the side wall 112 may have across-sectional shape that is circular, oval, polygonal, or other shape.The side wall 112 may have an inner dimension D1, such as but notlimited to an inner diameter or an inner width. In some embodiments, theinner dimension D1 of the side wall 112 may be generally constant in thevertical direction (i.e., +/−Z direction of the coordinate axis of FIGS.1A-1C) from the top of the side wall 112 to a flow control region 128.Alternatively, in other embodiments, the inner dimension D1 of the sidewall 112 may vary from the top of the innermost cylindrical container110 to the flow control region 128. As used in this disclosure, the term“cylindrical” is intended to include embodiments in which thecylindrical body is generally cylindrical but the inner dimension of thecylindrical body may vary along in the axial direction, such that theside walls of the cylindrical container are sloped, curved orirregular-shaped. In some embodiments, the side wall 112 of theinnermost cylindrical container 110 may be bell-shaped.

In the flow control region 128, the side wall 112, or the inner surface114 of the side wall 112, may slope inward (i.e., in the decreasing rdirection of the coordinate axis in FIGS. 1A-1C) towards an innermostdelivery ring 116. The innermost delivery ring 116 may extend verticallydownward (i.e, in the −Z direction of the coordinate axis of FIG. 1C)from the side wall 112 of the innermost cylindrical container 110 to adistal end 117 of the innermost delivery ring 116.

The innermost cylindrical container 110 may have a bottom wall 113 thatextends radially inward (i.e., in the decreasing r direction of thecoordinate axis of FIGS. 1A and 1C) from the side wall 112 to theinnermost delivery ring 116 extending downward (i.e., in the −Zdirection of the coordinate axis of FIGS. 1A and 1C) from the bottomwall 113. For example, in some embodiments, an outer surface 115 of theside wall 112 of the innermost cylindrical container 110 may slopeoutward (i.e., in the increasing r direction of the coordinate axis ofFIGS. 1A-1C), and the bottom wall 113 may extend between the outersurface 115 and the inner surface 114 of the side wall 112. In someembodiments, the bottom wall 113 may slope inward and verticallydownward from the outer surface 115 towards the inner surface 114 of theside wall 112. The innermost delivery ring 116 may define a centralopening 129 in the bottom wall 113 of the innermost cylindricalcontainer 110. The inner surface 114 of the side wall 112 may convergetoward a center axis A of the innermost cylindrical container 110 to theinnermost delivery ring 116. The innermost delivery ring 116 may be anannular ring that may provide an annular shape to molten glass flowingdown the surfaces of the innermost delivery ring 116.

Referring to FIGS. 1A and 1C, the apparatus 100 may include a blow tube120. The blow tube 120 may be a hollow tube that includes a head 122positioned at a proximal end 121 of the blow tube 120. The distal end ofthe blow tube 120 may be fluidly coupled to a gas source 416 (FIG. 11).A gas control valve 418 (FIG. 11) may be positioned between the gassource 416 and the distal end of the blow tube 120 to control the flowof gas delivered at the proximal end 121 of the blow tube 120. The blowtube 120 may be operable to deliver a gas flow at the innermost deliveryring 116. The head 122 of the blow tube 120 may be tapered so that thehead 122 of the blow tube 120 is bell-shaped. At least a portion of theblow tube 120 may be disposed in the innermost cylindrical container110. The proximal end 121 of the blow tube 120 may be positioned in theinnermost cylindrical container 110, and the blow tube 120 may bevertically oriented (i.e., in the +/−Z direction of the coordinate axisof FIGS. 1A and 1C) with the head 122 at the proximal end 121 positioneddownward (i.e., in the −Z direction) towards the innermost delivery ring116. In other words, the proximal end 121 of the blow tube 120 may bepositioned proximate the innermost delivery ring 116.

As illustrated in FIG. 1A, the blow tube 120 and the innermostcylindrical container 110 may define an inner annular chamber 124between the blow tube 120 and the inner surface 114 of the innermostcylindrical container 110. A molten glass composition may be introducedto the inner annular chamber 124 through at least one feed tube 118. Insome embodiments, the molten glass composition may be introduced to theinner annular chamber 124 from a single feed tube 118.

The head 122 of the blow tube 120 and the inner surface 114 of the sidewall 112 in the flow control region 128 of the innermost cylindricalcontainer 110 may define an annular flow channel 126 between the head122 and the inner surface 114 of the side wall 112 in the flow controlregion 128. The annular flow channel 126 may extend from the flowcontrol region 128 of the innermost cylindrical container 110 to theinnermost delivery ring 116. Molten glass introduced to the innerannular chamber 124 of the innermost cylindrical container 110 may flowfrom the flow control region 128, into the annular flow channel 126, andthrough the annular flow channel 126 to the innermost delivery ring 116.

The blow tube 120 may be translatable relative to the innermostcylindrical container 110. For example, in some embodiments, the blowtube 120 may be translatable in the vertical direction (i.e., in the+/−Z direction of the coordinate axis in FIGS. 1A and 1C) relative tothe innermost cylindrical container 110. Alternatively, in someembodiments, the blow tube 120 may be fixed in the vertical directionbut may be horizontally translatable (i.e., translatable in the +/−r or+/−θ directions of the coordinate axis of FIGS. 1A and 1C) relative tothe innermost cylindrical container 110. In still other embodiments, theblow tube 120 may be translatable in the vertical and horizontaldirections relative to the innermost cylindrical container 110.

Translation of the blow tube 120 relative to the innermost cylindricalcontainer 110 may control the flow rate, circumferential distribution,or both of the molten glass from the inner annular chamber 124 of theinnermost cylindrical container 110 to the innermost delivery ring 116.Translation of the blow tube 120 in the vertical direction (i.e., in the+/−Z direction of the coordinate axis of FIGS. 1A and 1C) changes theaverage width of the gap G1 between the head 122 of the blow tube 120and the inner surface 114 of the innermost cylindrical container 110 inthe flow control region 128. Vertical translation of the blow tube 120is indicated in FIG. 1C by the vertical double-arrow 188 positionedabove the blow tube 120. Changing the width of the gap G1 throughtranslation of the blow tube 120 in the vertical direction may changethe impedance to flow of the molten glass through the annular flowchannel 126, thereby changing the flow rate of the molten glass throughthe annular flow channel 126 to the innermost delivery ring 116.Changing the flow rate of the molten glass through the annular flowchannel 126 to the innermost delivery ring 116 may change the thicknessof the glass layer associated with the innermost cylindrical container110.

Additionally, translation of the blow tube 120 horizontally (i.e., inthe +/−r or +/−θ directions of the cylindrical coordinate axis of FIGS.1A and 1C) relative to the fixed position of the innermost cylindricalcontainer 110 may change the width of the gap G1 around thecircumference of the head 122 of the blow tube 120. Horizontaltranslation of the blow tube 120 is indicated in FIG. 1C by thehorizontally oriented double-arrow 189 positioned above the blow tube120. In other words, horizontal translation of the blow tube 120relative to the innermost cylindrical container 110 may offset the blowtube 120 from the center axis A of the innermost cylindrical container110 so that the blow tube 120 ceases to be concentric with respect tothe 110. Thus, the width of the gap G1 varies around the circumferenceof the head 122 of the blow tube 120. Translating the blow tube 120horizontally relative to the innermost cylindrical container 110 maycontrol the circumferential distribution of the molten glass flowingthrough the annular flow channel 126. In other words, onecircumferential region of the annular flow channel 126 may have adifferent flow rate of molten glass than another circumferential regionof the annular flow channel 126.

Controlling the circumferential distribution of the molten glass flowingthrough the annular flow channel 126 to the innermost delivery ring 116may enable control of the circumferential thickness of the glass layerproduced by the innermost cylindrical container 110. Controlling thecircumferential distribution of the molten glass flowing between thehead 122 of the blow tube 120 and the inner surface 114 of the innermostcylindrical container 110 may also enable the apparatus 100 tocompensate for differences in the level of molten glass in the innermostcylindrical container 110 caused by off-centered positioning of thesingle feed tube 118 relative to the innermost cylindrical container110.

Referring to FIGS. 1A-1C, the first outer cylindrical container 130 mayinclude a side wall 132 and a bottom wall 133. The side wall 132 of thefirst outer cylindrical container 130 may have an inner dimension D2,such as but not limited to an inner diameter or an inner width, that isgreater that than the inner dimension D1 of the innermost cylindricalcontainer 110. In some embodiments, the inner dimension D2 of the sidewall 132 may be greater than an outer dimension of the innermostcylindrical container 110. The first outer cylindrical container 130 maybe concentrically arranged around the innermost cylindrical container110. In some embodiments, the first outer cylindrical container 130 mayfully surround the innermost cylindrical container 110. The first outercylindrical container 130 may be concentric about the center axis A ofthe innermost cylindrical container 110. The position of the first outercylindrical container 130 may be fixed relative to the position of theinnermost cylindrical container 110. The side wall 132 of the firstouter cylindrical container 130 may be cylindrical in shape. When viewedin top view, the side wall 132 may have a cross-section that iscircular, oval, polygonal, or other shape. In some embodiments, theinner dimension D2 of the side wall 132 may be generally constant in thevertical direction (i.e., +/−Z direction of the coordinate axis of FIGS.1A-1C) from the top of the side wall 132 to a flow control region 144 ofthe first outer cylindrical container 130. Alternatively, in otherembodiments, the inner dimension D2 of the side wall 132 may changeslightly from the top of the side wall 132 of the first outercylindrical container 130 to the flow control region 144 of the firstouter cylindrical container 130.

The first outer cylindrical container 130 may have a bottom wall 133that may extend from the side wall 132 to a first outer delivery ring136. In some embodiments, the bottom wall 133 may extend radially inward(i.e., in the decreasing r direction of the coordinate axis of FIGS. 1Aand 1C) from the side wall 132 to the first outer delivery ring 136.Alternatively, in some embodiments, the bottom wall 133 may extendradially inward and vertically downward (i.e., in the +/−Z direction ofthe coordinate axis of FIGS. 1A and 1C) from the side wall 132 to thefirst outer delivery ring 136.

Referring to FIGS. 1A and 1C, the first outer delivery ring 136 mayextend vertically downward (i.e., in the −Z direction) from the bottomwall 133 of the first outer cylindrical container 130 to define acentral opening in the bottom wall 133 of the first outer cylindricalcontainer 130. The first outer delivery ring 136 may be an annular ringthat provides an annular shape to molten glass flowing down the surfacesof the first outer delivery ring 136 and between the first outerdelivery ring 136 and the innermost delivery ring 116. The first outerdelivery ring 136 may terminate in a distal end of the first outerdelivery ring 136. The first outer delivery ring 136 may be larger thanthe innermost delivery ring 116 so that the first outer delivery ring136 may surround the innermost delivery ring 116. The first outerdelivery ring 136 may be spaced apart from the innermost delivery ring116 to allow molten glass to flow between the first outer delivery ring136 and the innermost delivery ring 116.

In some embodiments, each successive outer delivery ring, such as thedelivery ring 136 extending from the first outer cylindrical container130 or a delivery ring 156 extending from a second outer cylindricalcontainer 150, may extend further downward (i.e., −Z direction of thecoordinate axis of FIG. 4A) relative to the innermost delivery ring 116.For example, referring to FIG. 1C, in some embodiments, the distal end137 of the first outer delivery ring 136 may extend from the bottom wall133 of the first outer cylindrical container 130 so that the distal end137 of the first outer delivery ring 136 is vertically below the distalend 117 of the innermost delivery ring 116 extending from the innermostcylindrical container 110.

The side walls of adjacent cylindrical containers 102 of the apparatus100, such as the side wall 112 of the innermost cylindrical container110 and the side wall 132 of the first outer cylindrical container 130,may define an annular chamber between the side walls. Referring to FIG.1C, the side wall 112 of the innermost cylindrical container 110 and theside wall 132 of the first outer cylindrical container 130 may define anannular chamber 140. The annular chamber 140 may be defined between theinner surface 134 of the side wall 132 and the outer surface 115 of theside wall 112. The annular chamber 140 may extend vertically downward(i.e, in the −Z direction of the coordinate axis of FIG. 1C) from thetop ends of the innermost cylindrical container 110 and first outercylindrical container 130 to a flow control region 144. The annularchamber 140 provides an annular volume to receive a quantity of moltenglass for producing a glass layer of the composite glass tube. The sidewall 132 of the first outer cylindrical container 130 may be spacedapart from the side wall 112 of the innermost cylindrical container 110by a distance C1 measured between the inner surface 134 of the side wall132 and the outer surface 115 of the side wall 112. In some embodiments,the distance C1 between the inner surface 134 of the side wall 132 andthe outer surface 115 of the side wall 112 may be substantially constantalong a vertical dimension of the annular chamber 140.

The side walls or the bottom walls of the adjacent cylindricalcontainers 102, such as the innermost cylindrical container 110 and thefirst outer cylindrical container 130, may define the flow controlregion 144 at the lower end of the annular chamber 140 (i.e., the end ofthe annular chamber in the −Z direction). For example, the side wall 112of the innermost cylindrical container 110 and the side wall 132 of thefirst outer cylindrical container 130 may converge to form the flowcontrol region 144, which comprises a narrowed section in which thedistance between the side walls or bottom walls is less than thedistance between the side walls in the annular chamber 140. In someembodiments, in the flow control region 144, the distance C1 between theside walls or the bottom walls may vary through the flow control region144 as shown in FIG. 1C. Alternatively, in other embodiments, thedistance C1 between the side walls or the bottom walls may be constantthroughout the flow control region 144 as shown in FIGS. 5A-5C.

Referring to FIG. 1C, in some embodiments, the side wall 132 of thefirst outer cylindrical container 130 and the side wall 112 of theinnermost cylindrical container 110 define the flow control region 144.The flow control region 144 may extend from the annular chamber 140 toan annular flow channel 142 defined between the bottom wall 133 of thefirst outer cylindrical container 130 and the bottom wall 113 of theinnermost cylindrical container 110. In the flow control region 144, thedistance C1 between the inner surface 134 of the side wall 132 and theouter surface 115 of the side wall 112 may decrease from a maximumdistance C1 at the entrance to the flow control region 144 proximate tothe annular chamber 140 to a minimum distance C2 at the exit of the flowcontrol region 144 to the annular flow channel 142.

In some embodiments, in the flow control region 144, the inner surface134 of the side wall 132 may slope inward (i.e., in the decreasing rdirection of the coordinate axis of FIG. 1C) towards the outer surface115 of the side wall 112. Alternatively, in other embodiments, in theflow control region 144, the outer surface 115 of the side wall 112 mayslope outward (i.e., in the increasing r direction of the coordinateaxis of FIG. 1C) towards the inner surface 134 of the side wall 132. Instill other embodiments, the inner surface 134 of the side wall 132slopes inward and the outer surface 115 of the side wall 112 slopesoutward so that the inner surface 134 of the side wall 132 and the outersurface 115 of the side wall 112 converge toward each other as the sidewall 112 and the side wall 132 extend vertically downward towards theannular flow channel 142. In some embodiments, the slope of the innersurface 134 of the side wall 132, the slope of the outer surface 115 ofthe side wall 112, or both may be constant through the flow controlregion 144. Alternatively, in other embodiments, the slope of the innersurface 134 of the side wall 132, the slope of the outer surface 115 ofthe side wall 112, or both may vary through the flow control region 144from the annular chamber 140 to the annular flow channel 142. Forexample, the inner surface 134 of the side wall 132, the outer surface115 of the side wall 112, or both may be curved or irregular-shaped inthe flow control region 144. In some embodiments, the slope of the innersurface 134 of the side wall 132 may be a mirror image (e.g., equalslope but opposite sign) of the slope of the outer surface 115 of theside wall 112. Alternatively, the slope of the inner surface 134 of theside wall 132 and the slope of the outer surface 115 of the side wall112 may have different shapes. In some embodiments, the inner surface134 of the side wall 132 or the outer surface 115 of the side wall 112may be substantially vertical (i.e., parallel to central axis A of theapparatus 100).

Referring to FIGS. 5A-5C, in some embodiments, in the flow controlregion 144, the inner surface 134 of the side wall 132 and the outersurface 115 of the side wall 112 may be parallel throughout the flowcontrol region 144. In these embodiments, the distance C1 between theinner surface 134 of the side wall 132 and the outer surface 115 of theside wall 112 may be constant in the flow control region 144. In otheralternative embodiments, the bottom wall 133 of the first outercylindrical container 130 and the bottom wall 113 of the innermostcylindrical container 110 may define the flow control region 144. Inthese embodiments, the distance between the bottom wall 113 of theinnermost cylindrical container 110 and the bottom wall 133 of the firstouter cylindrical container 130 may decrease as the bottom wall 113 andthe bottom wall 133 extend radially inward towards the center axis A ofthe apparatus 100. In still other embodiments, the distance between thebottom wall 113 of the innermost cylindrical container 110 and thebottom wall 133 of the first outer cylindrical container 130 may beconstant throughout the flow control region 144 defined between thebottom wall 113 and the bottom wall 133.

The bottom walls of adjacent cylindrical containers 102 may defineannular flow channels extending inward from the flow control region tothe delivery rings of the adjacent cylindrical containers. Referring toFIG. 1C, the bottom wall 113 of the innermost cylindrical container 110and the bottom wall 133 of the first outer cylindrical container 130 maydefine the annular flow channel 142. The annular flow channel 142 may bedefined to extend inward (i.e., in the decreasing r direction of thecoordinate axis of FIG. 1C) from the flow control region 144 to thefirst outer delivery ring 136 of the first outer cylindrical container130. In some embodiments, at least a portion of the annular flow channel142 may be defined between the side wall 112 of the innermostcylindrical container 110 and the side wall 132 of the first outercylindrical container 130 so that molten glass flowing through theannular flow channel 142 may flow vertically downward (i.e., in the −Zdirection) from the flow control region 144 and then may flow inwardtowards the center axis A of the apparatus 100 and the first outerdelivery ring 136 of the first outer cylindrical container 130.

Referring to FIGS. 1A-1C, the apparatus may also have a second outercylindrical container 150. The second outer cylindrical container 150may include a side wall 152 and a bottom wall 153. The side wall 152 ofthe second outer cylindrical container 150 may have an inner dimensionD3, such as but not limited to an inner diameter or an inner width, thatis greater that than the inner dimension D2 of the first outercylindrical container 130. In some embodiments, the inner dimension D3of the side wall 152 may be greater than an outer dimension of the firstouter cylindrical container 130. The second outer cylindrical container150 may be concentrically arranged around the first outer cylindricalcontainer 130. In some embodiments, the second outer cylindricalcontainer 150 may fully surround the first outer cylindrical container130. The second outer cylindrical container 150 may be concentric aboutthe center axis A of the innermost cylindrical container 110 and thefirst outer cylindrical container 130. The position of the second outercylindrical container 150 may be fixed relative to the position of theinnermost cylindrical container 110 and the first outer cylindricalcontainer 130. The side wall 152 of the second outer cylindricalcontainer 150 may have a shape similar to the shapes previouslydescribed for the side wall 132.

The second outer cylindrical container 150 may have a bottom wall 153that may extend from the side wall 152 to a second outer delivery ring156. In some embodiments, the bottom wall 153 may extend radially inward(i.e., in the decreasing r direction of the coordinate axis of FIGS. 1Aand 1C) from the side wall 152 to the second outer delivery ring 156.Alternatively, in some embodiments, the bottom wall 153 may extendradially inward and vertically downward (i.e., in the +/−Z direction ofthe coordinate axis of FIGS. 1A and 1C) from the side wall 152 to thesecond outer delivery ring 156.

Referring to FIGS. 1A and 1C, the second outer delivery ring 156 mayextend vertically downward (i.e., in the −Z direction) from the bottomwall 153 of the second outer cylindrical container 150 to define acentral opening in the bottom wall 153 of the second outer cylindricalcontainer 150. The second outer delivery ring 156 may be an annular ringthat provides an annular shape to molten glass flowing down the surfacesof the second outer delivery ring 156 and between the second outerdelivery ring 156 and the first outer delivery ring 136. The secondouter delivery ring 156 may terminate in a distal end 157 of the secondouter delivery ring 156. The second outer delivery ring 156 may belarger than the first outer delivery ring 136 so that the second outerdelivery ring 156 may surround the first outer delivery ring 136. Thesecond outer delivery ring 156 may be spaced apart from the first outerdelivery ring 136 to allow molten glass to flow between the second outerdelivery ring 156 and the first outer delivery ring 136.

An inner surface 154 of the side wall 152 of the second outercylindrical container 150 and an outer surface 135 of the side wall 132of the first outer cylindrical container 130 may define an annularchamber 160 and flow control region 164 between the annular chamber 160and an annular flow channel 162. The bottom wall 153 of the second outercylindrical container 150 and the bottom wall 133 of the first outercylindrical container 130 may define the annular flow channel 162. Theannular chamber 160, annular flow channel 162, and the flow controlregion 164 may have any of the features or attributes previouslydescribed in relation to the annular chamber 140, annular flow channel142, and the flow control region 144 defined between the first outercylindrical container 130 and the innermost cylindrical container 110.

The apparatus 100 may have additional cylindrical containers 102 havingincreasing inner dimensions and arranged concentrically around thesecond outer cylindrical container 150. For example, in someembodiments, the apparatus 100 may have 1, 2, 3, 4, 5, 6, 7, or morethan 7 cylindrical containers 102. Referring to FIG. 2, in oneembodiment, the apparatus 100 may have five cylindrical containers 102,which may be utilized to produce a composite glass tube having up to 5glass layers. Referring to FIG. 19, the apparatus 100 may have 2cylindrical containers 102 to produce composite glass tubes having 2glass layers. The side walls, bottom walls, delivery rings, annularchambers, annular flow channels, and flow control regions of eachsuccessive cylindrical container may include features and attributes aspreviously described in this disclosure in relation to the first outercylindrical container 130.

The position of each cylindrical container 102, such as the innermostcylindrical container 110, the first outer cylindrical container 130,and the second outer cylindrical container 150, is fixed relative to theother cylindrical containers 102. For example, each of the cylindricalcontainers 102 may be fixed relative to the other cylindrical containers102 by coupling the cylindrical containers 102 to each other using aplurality of struts 180. Referring again to FIGS. 1A-1C, fixing thepositions of the innermost cylindrical container 110, first outercylindrical container 130, and second outer cylindrical container 150relative to each other may maintain the shape of each of the innermostcylindrical container 110, the first outer cylindrical container 130,and the second outer cylindrical container 150 during heat up andoperation of the apparatus 100. Structurally fixing the variouscylindrical containers 102 to each other helps guide thermal expansionto minimize deformation of original shapes of the cylindrical containersand of the volumes defined in-between the cylindrical containers 102.During normal operation of the apparatus 100, the cylindrical containers102 are subjected to mechanic and thermal stresses, which could deformshapes. Deformation of the cylindrical containers 102 during normaloperation is also reduced by providing structural rigidity to thecylindrical containers 102, such as by fixing them to each other. Fixingthe positions of the innermost cylindrical container 110, the firstouter cylindrical container 130, and the second outer cylindricalcontainer 150 relative to each other may also enable independent controlof the thickness of a glass layer associated with the first outercylindrical container 130 or the second outer cylindrical container 150without disrupting or changing the thickness of any of the other glasslayers.

Referring to FIGS. 1A and 1C, the apparatus 100 may include a pluralityof feed tubes 118 for delivering molten glass to each of the cylindricalcontainers 102. In some embodiments, the apparatus 100 may include asingle feed tube 118 for each one of the plurality of cylindricalcontainers 102. For example, in FIGS. 1A and 1C, each of the innermostcylindrical container 110, the first outer cylindrical container 130,and the second outer cylindrical container 150 have a single feed tube118. Each feed tube 118 may be fluidly coupled to a molten glass system424 (FIG. 11). In some embodiments, the feed tube 118 may be a flowconduit fluidly coupling the molten glass system 424 to one of thecylindrical containers 102. The feed tubes 118 may enable continuousintroduction of molten glass compositions to each of the cylindricalcontainers 102, thereby enabling continuous operation of the apparatus100. In some embodiments, one or a plurality of the feed tubes 118 maybe fluidly coupled to separate molten glass systems so that differentglass compositions may be introduced to one or more than one of thecylindrical containers 102.

Separate feed tubes 118 for each cylindrical container 102 may enablethe level of molten glass in each cylindrical container 102 to beindependent of the level of molten glass in each of the othercylindrical containers 102. Positioning a single feed tube 118 in eachcylindrical container 102 may produce a circumferential distribution ofthe level of molten glass in each cylindrical container 102. Thevariation in the level of molten glass around the circumference of thecylindrical container 102 may be compensated for by changing thepositions of each of the flow control valves 170 relative to each of theother flow control valves 170 associated with the cylindrical container102. Operation of the control valves 170 will be further describedherein.

Referring to FIG. 1A, the apparatus 100 may include a plurality ofstruts 180 coupled between one or a plurality of the cylindricalcontainers 102. The struts 180 may maintain the fixed position of eachof the cylindrical containers 102 and may provide structural support tothe cylindrical containers 102 to reduce the strain on the cylindricalcontainers 102 during operation. As shown in FIG. 1A, the struts 180 mayextend horizontally (i.e., radially or in the +/−r direction of thecoordinate axis of FIGS. 1A and 1B) between the innermost cylindricalcontainer 110 and the first outer cylindrical container 130 and betweenthe first outer cylindrical container 130 and the second outercylindrical container 150. In some embodiments, the struts 180 may bedistributed vertically so that multiple struts 180 at different verticalpositions (i.e., positions in the +/−Z direction of the coordinate axisof FIGS. 1A and 1C) extend horizontally between the innermostcylindrical container 110 and the first outer cylindrical container 130and between the first outer cylindrical container 130 and the secondouter cylindrical container 150. Additionally, the struts 180 may becircumferentially distributed around the apparatus 100. The struts 180may be distributed about the cylindrical containers 102 in positionsthat do not obstruct movement of the flow control valves 170 relative tothe cylindrical containers 102, as will be further described herein.

Referring to FIGS. 1A-1C, the apparatus 100 may include a plurality offlow gussets 182 disposed in one or a plurality of the annular flowchannels (e.g., annular flow channel 142 and annular flow channel 162).For example, the flow gussets 182 may be disposed in the annular flowchannel 142. Each of the flow gussets 182 may be coupled to theinnermost cylindrical container 110 and the first outer cylindricalcontainer 130 so that each of the flow gussets 182 bisects the annularflow channel 142 defined between the innermost cylindrical container 110and the first outer cylindrical container 130. The flow gussets 182 mayextend from the flow control region 144, through the annular flowchannel 142, to the delivery ring 136 of the first outer cylindricalcontainer 130. In some embodiments, each flow gusset 182 may extend tothe distal end 137 of the delivery ring 136. In some embodiments, theflow gussets 182 may extend up into at least a portion of the flowcontrol region 144. In still other embodiments, the flow gussets 182 mayextend through the entire flow control region 144. The flow gussets 182may have any cross-sectional shape. In some embodiments, the flowgussets 182 may be generally flat. Alternatively, in other embodiments,the flow gussets 182 may have a cross-sectional profile that varies fromthe flow control region 144 to the delivery ring 136. For example, insome embodiments, the thickness of the flow gussets 182 may vary alongthe annular flow channel 142 from the flow control region 144 to thedelivery ring 136. Other shapes for the flow gussets 182 arecontemplated.

The flow gussets 182 may separate the annular flow channel 142, andoptionally the flow control region 144, into a plurality of angularsectors 184. In some embodiments, the flow gussets 182 may be evenly andcircumferentially distributed throughout the annular flow channel 142.Alternatively, in other embodiments, the flow gussets 182 may beirregularly spaced throughout the annular flow channel 142 to producethe angular sectors 184 having different angular dimensions.

The flow gussets 182 may physically separate the molten glass flowingthrough each angular sector 184 to maintain the impedance to flowcreated by each of the flow control valves 170 until the molten glassesfrom each of the angular sectors 184 converges at the delivery ring 136,where the flow gussets 182 terminate. The flow gussets 182 may maintainthe circumferential flow distribution of molten glass produced by theflow control valves 170. The molten glass streams merge into a singleannular flow of molten glass at the terminal end 183 of the flow gussets182. The terminal end 183 of the flow gussets 182 may be proximate tothe distal end 137 of the delivery ring 136.

Flow gussets 182 may also be disposed in the annular flow channel 162and, optionally, the flow control region 164 defined between the firstouter cylindrical container 130 and second outer cylindrical container150. Likewise, flow gussets 182 may be disposed in the annular channeland, optionally, the flow control region defined between any twoadjacent cylindrical containers 102.

Referring to FIGS. 1A and 1C, the apparatus 100 may include at least oneflow control valve 170 to control the flow rate of molten glass from theannular chamber 140, through the flow control region 144, and throughthe annular flow channel 142. The flow control valves 170 will bedescribed in this disclosure in the context of the first outercylindrical container 130 and the annular chamber 140, annular flowchannel 142, and flow control region 144 defined between the first outercylindrical container 130 and the innermost cylindrical container 110.However, it is understood that the flow control valves 170 positioned inother of the cylindrical containers 102, such as second outercylindrical container 150, may include the same features and operationas those described herein in association with the first outercylindrical container 130.

Referring to FIGS. 3A-3C, each of the flow control valves 170 mayinclude a control element 172 coupled to a shaft 174. The controlelement 172 may have a shape complimentary to the contours of the innersurface 134 of the first outer cylindrical container 130 or the outersurface 115 of the innermost cylindrical container 110. In someembodiments, the control element 172 may be a plug elongated in theangular direction (i.e., in the +/−θ direction of the coordinate axis ofFIGS. 3A-3C) and having at least one control surface 176 shaped toconform to the inner surface 134 of the first outer cylindricalcontainer 130, the outer surface 115 of the innermost cylindricalcontainer 110, or both in the flow control region 144 defined betweenthe first outer cylindrical container 130 and the innermost cylindricalcontainer 110. Referring to FIG. 3B, a cross-sectional view of oneembodiment of the control element 172 disposed within the flow controlregion 144 between the first outer cylindrical container 130 and theinnermost cylindrical container 110 is schematically depicted. In someembodiments, the control element 172 may include two control surfaces176 extending downward (i.e., in the −Z direction of the coordinate axisof FIG. 3B) and converging at a point. The control surfaces 176 may besloped and the slopes of the control surfaces 176 may be complimentaryto the inner surface 134 of the first outer cylindrical container 130and the outer surface 115 of the innermost cylindrical container 110 inthe flow control region 144. Alternatively, in other embodiments, thecontrol element 172 may include a wedge, flap, gate, or other structurethat may be engageable with the flow control region 144 defined betweenthe first outer cylindrical container 130 and the innermost cylindricalcontainer 110.

Referring to FIGS. 5A-5C, in other embodiments, the control element 172may have a width measured in the radial direction (i.e., it the +/−rdirection of the coordinate axis in FIG. 5A) that is constant withrespect to the vertical direction (i.e., in the +/Z direction). Forexample, in some embodiments, the control surfaces of the controlelement 172 of the flow control valve 170 may be parallel to the outersurface 115 of the innermost cylindrical container 110 and the innersurface 134 of the first outer cylindrical container 110 in the flowcontrol region 144. Other shapes for the control element 172 may also besuitable for changing the impedance to flow of molten glass through theflow control region 144.

Referring back to FIGS. 3A and 3C, in some embodiments, thecross-sectional shape of the first outer cylindrical container 130 maybe generally circular, and the control element 172 may be arcuate inshape (i.e., having a constant radial dimension relative to the centeraxis A of the apparatus 100) and may include a radial dimension and anangular dimension corresponding to the flow control region 144.Referring to FIG. 3C, for example, the control element 172 of the flowcontrol valve 170 may have a radius R1 measured from the center axis Aof the apparatus 100 and an angular dimension β relative to the centeraxis A of the apparatus. The radius R1 of the control element 172 may besufficient to ensure that a midsagittal plane P of the control element172 is vertically aligned (i.e., in the +/−Z direction of the coordinateaxis of FIGS. 3A-3C) with the center of the flow control region 144throughout the angular dimension β of the control element. The angulardimension β of the control element 172 may be less than the angulardimension α of the angular sector 184 so that the control element 172can be positioned between the flow gussets 182 defining the angularsector 184. The difference between the angular dimension α of theangular sector 184 and the angular dimension β of the control element172 may be sufficient to allow the control element 172 to move freelybetween the flow gussets 182 but not so great that a substantialquantity of molten glass is permitted to flow between the ends of thecontrol element 172 and the flow gussets 182 without flowing between thecontrol element 172 and the inner surface 134 of the first outercylindrical container 130 or the outer surface 115 of the innermostcylindrical container 110.

The shaft 174 may be coupled to the control element 172 and may extendvertically upward (i.e., in the +Z direction of the coordinate axis ofFIGS. 3A-3B). In some embodiments, the shaft 174 may be coupled to thecontrol element 172 at a midpoint 173 of the control element 172.Although depicted and described as having a single shaft 174, it isunderstood that each of the flow control valves 170 may include aplurality of shafts 174 coupled to the control element 172 and extendingupward therefrom.

In some embodiments, the flow control valves 170, including the controlelement 172 and/or the shaft 174 may be constructed of electricallyconductive refractory metals. Electrically conductive refractory metalsmay include platinum or platinum-containing metals such asplatinum-rhodium, platinum-iridium, dispersed hardened platinummaterials, and combinations thereof. For example, in some embodiments,the flow control valves 170 may include platinum. In some embodiments,the flow control valves 170 may include dispersed hardened platinum.Other refractory metals may include molybdenum, palladium, rhenium,tantalum, titanium, tungsten, ruthenium, osmium, zirconium, and alloysthereof and/or zirconium dioxide. Alternatively, in other embodiments,the flow control valves 170 may include other refractory materials, suchas, but not limited to zircon (e.g., zirconia), silicon carbide,xenotime, alumina-based refractory ceramics, aluminosilicate refractoryceramics, other refractory materials, or combinations of these. In someembodiments, the flow control valves 170 may include a refractoryceramic material cladded with a refractory metal.

Referring to FIGS. 4A-4C, each flow control valve 170 may be disposed inthe first outer cylindrical container 130 with the control element 172positioned proximate to the flow control region 144 defined between thefirst outer cylindrical container 130 and the innermost cylindricalcontainer 110. The shaft 174 may extend vertically upward (i.e., in the+Z direction of the coordinate axis of FIGS. 4A-4C) through the annularchamber 140 and above the tops of the first outer cylindrical container130 and innermost cylindrical container 110. With the control element172 positioned proximate to the flow control region 144, the controlsurface 176 of the control element 172 and the inner surface 134 of thefirst outer cylindrical container 130, the outer surface 115 of theinnermost cylindrical container 110, or both may define a gap G2 betweenthe control surface 176 of the control element 172 and the inner surface134 of the first outer cylindrical container 130 and/or the outersurface 115 of the innermost cylindrical container 110.

In some embodiments, the apparatus 100 may include a plurality of flowcontrol valves 170. In some embodiments, the number of flow controlvalves 170 associated with each cylindrical container, such as the firstouter cylindrical container 130, may be equal to the number of flowgussets 182 disposed in the annular flow channel defined by thatcylindrical container 102. In some embodiments, the number of flowcontrol valves 170 associated with the first outer cylindrical container130 may be equal to the number of flow gussets 182 positioned in theannular flow channel 142 defined between the first outer cylindricalcontainer 130 and the innermost cylindrical container 110. The apparatus100 may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more than 12 flowcontrol valves 170 disposed between two adjacent cylindrical containers,such as between the innermost cylindrical container 110 and the firstouter cylindrical container 130. For example, referring to FIG. 6A, insome embodiments, the first outer cylindrical container 130 may includetwo flow gussets 182 and two flow control valves 170, each of the twoflow control valves 170 associated with one of the two angular sectors184 defined by the flow gussets 182. Referring to FIG. 6B, in otherembodiments, the first outer cylindrical container 130 may have 3 flowcontrol valves 170 with each of the flow control valves 170 positionedin one of the angular sectors 184 defined by the flow gussets 182.Referring to FIG. 1B, the first outer cylindrical container 130 may have4 flow control valves 170. Referring to FIGS. 6C and 6D, in otherembodiments, the first outer cylindrical container 130 may have 6 flowcontrol valves 170 or 8 flow control valves 170, respectively. In stillother embodiments, the first outer cylindrical container 130 may havemore than 8 flow control valves 170. The flow control valves 170 may beevenly and circumferentially distributed around the first outercylindrical container 130. As the number of flow gussets 182 and flowcontrol valves 170 for the first outer cylindrical container 130increases, the ability to adjust the circumferential glass flowdistribution of the glass layer associated with the first outercylindrical container 130 may also increase. Similarly, increasing thenumber of flow gussets 182 and flow control valves 170 for any of thecylindrical containers 102 may improve the ability to adjust thecircumferential glass flow distribution of the glass layer associatedwith the cylindrical container 102.

Referring to FIGS. 4A-4C, as previously described, each of the pluralityof flow control valves 170 may be translatable relative to the innermostcylindrical container 110 and the first outer cylindrical container 130to change impedance to flow of the molten glass through the flow controlregion 144. The plurality of flow control valves 170 may be translatedin the vertical direction (i.e., in the +/−Z direction), the radialdirection (i.e., in the +/−r direction of the coordinate axis in FIGS.4A-4C), the angular direction (i.e., in the +/−θ direction of thecoordinate axis of FIGS. 4A-4C, such as by rotating the flow controlvalve 170 about the axis A (FIG. 1C) of the apparatus 100), orcombinations of these. Translation of the flow control valves 170relative to the first outer cylindrical container 130 may change theshape of the gap G2 defined between the control element 172 and theinner surface 134 of the side wall 132 and the outer surface 115 of theside wall 112. For example, translation of the flow control valve 170 inthe vertical, radial, and/or angular dimensions relative to the firstouter cylindrical container 130 may change the radial width, verticallength, and/or angular length of the gap G2, thereby changing theimpedance to flow of the molten glass through the flow control region144.

For example, referring to FIGS. 4A-4C, in some embodiments, the flowcontrol valve 170 may be vertically translatable (i.e., in the +/−Zdirection) relative to the innermost cylindrical container 110 and firstouter cylindrical container 130. Vertical translation of the flowcontrol valves 170 relative to the first outer cylindrical container 130is indicated in FIGS. 4A-4C by the vertically oriented double arrows 198next to the flow control valve 170. Translation of the flow controlvalve 170 relative to the innermost cylindrical container 110 and firstouter cylindrical container 130 may cause the control element 172 tomove in the flow control region 144 relative to the innermostcylindrical container 110 and first outer cylindrical container 130 todecrease or increase a width of the gap G2 defined between the controlsurface 176 of the control element 172 and the inner surface 134 of thefirst outer cylindrical container 130 and/or the outer surface 115 ofthe innermost cylindrical container 110. Each of the flow control valves170 may also be independently translatable relative to each of the otherflow control valves 170 associated with the first outer cylindricalcontainer 130, thereby enabling the gap G2 to vary from between the flowcontrol valves 170 of the first outer cylindrical container 130.

Referring now to FIGS. 5A-5C, in other embodiments, the distance C1 maybe constant through the flow control region 144 and the control element172 of the flow control valve 170 may have control surfaces that aregenerally parallel to the inner surface 134 of the side wall 132 and theouter surface 115 of the side wall 112 in the flow control region 144.In these embodiments, vertical translation of the flow control valve 170relative to the first outer cylindrical container 130 may increase thelength L of the gap G2 between the control element 172 and the innersurface 134 of the side wall 132 and the outer surface 115 of the sidewall 112. The radial width of gap G2 may remain constant withtranslation of the flow control valve 170 relative to the first outercylindrical container 130.

FIG. 4B schematically depicts operation of the first outer cylindricalcontainer 130 and the flow control valves 170 of the apparatus 100 toproduce a glass layer of the composite glass tube from a molten glasscomposition. Referring to FIG. 4B, the molten glass composition may beintroduced to the first outer cylindrical container 130 through the feedtube 118. The molten glass composition may flow downward (i.e., in the−Z direction of the coordinate axis in FIG. 4B) by the force of gravitythrough the annular chamber 140 defined between the first outercylindrical container 130 and the innermost cylindrical container 110.Additionally, the molten glass composition may flow circumferentially(i.e., in the +/−θ direction of the coordinate axis of FIG. 4B) aroundthe annular chamber 140 to distribute the molten glass compositionthroughout the annular chamber 140. In the flow control region 144, themolten glass composition may flow around the control element 172 of eachof the flow control valves 170 and through the gap G2 defined betweenthe control surface 176 of the control element 172 and the inner surface134 of the first outer cylindrical container 130 and/or the outersurface 115 of the innermost cylindrical container 110.

Once it passes through the gap G2, the molten glass composition may flowinto and through the annular flow channel 142 from the flow controlregion 144 to the first outer delivery ring 136. As previouslydescribed, the molten glass composition in each angular sector 184 ofthe annular flow channel 142 defined by the flow gussets 182 may bephysically separated from the molten glass composition in each of theother angular sectors 184 of the annular flow channel 142 as the moltenglass composition flows through the annular flow channel 142. Thus, flowof the molten glass composition through the annular flow channel 142 maybe generally radially inward towards the first outer delivery ring 136.Circumferential flow of the molten glass in the annular flow channel 142may be substantially prevented by the flow gussets 182.

Referring to FIG. 7A, at the terminal end 183 of the flow gussets 182,the streams of the molten glass composition from each angular sector 184may recombine at the first outer delivery ring 136. The molten glasscomposition then flows generally downward (i.e., in the −Z direction ofthe coordinate axis of FIG. 7A) along the inner surface of the firstouter delivery ring 136 in an annular shaped flow. At the distal end 137of the first outer delivery ring 136, the molten glass composition mayseparate from the first outer delivery ring 136 to form a glass layer214 of the molten glass composition 204, which may converge with otherglass layers to form the composite glass tube 200.

Referring again to FIGS. 4A-4B, translating the flow control valve 170relative to the first outer cylindrical container 130 and innermostcylindrical container 110 to increase or decrease the width of the gapG2 may increase or decrease the impedance to flow of the molten glassthrough the flow control region 144 and into the annular flow channel142 defined between the first outer cylindrical container 130 and theinnermost cylindrical container 110. For example, in FIG. 4A, thecontrol element 172 is positioned close to the flow control region 144so that the gap G2 is smaller and the impedance to flow of the moltenglass between the control element 172 and the first outer cylindricalcontainer 130 and/or innermost cylindrical container 110 is greatercompared to the position of the flow control valve 170 in FIG. 4B. InFIG. 4B, the control element 172 is positioned further away from theflow control region 144, thereby increasing the width of the gap G2 anddecreasing the impedance to the flow of molten glass. In FIG. 4C, theflow control valve 170 is positioned at a maximum distance from the flowcontrol region 144, thereby increasing the width of the gap G2 to amaximum width, at which the impedance to flow of molten glass betweenthe control element 172 and the first outer cylindrical container 130and/or the innermost cylindrical container 110 is at a minimum.Increasing or decreasing the impedance to flow of the molten glassthrough the flow control region 144 by translating the flow controlvalve 170 relative to the first outer cylindrical container 130 and/orinnermost cylindrical container 110 may increase or decrease,respectively, the flow rate of molten glass through the flow controlregion 144 and into the annular flow channel 142.

For a given glass level, the maximum flow rate of molten glass throughthe flow control region 144 is attained when the flow control valve 170is positioned at its highest position such that the gap G2 is at itsmaximum width. The minimum position of the flow control valve 170 may bea position below which the flow of molten glass through the flow controlregion 144 is insufficient to sustain the flow rate of molten glassdownstream of the flow control region 144, such as through the annularflow channel 142 and down the first outer delivery ring 136. Referringto FIGS. 9A and 9B, the results of a 2D axis symmetric flow model ofmolten glass through the flow control region 144 and the annular flowchannel 142 defined by the first outer cylindrical container 130 isprovided. The 2D axis symmetric flow model was built using commerciallyavailable fluid dynamics modeling software available from COMSOL. FIG.9A graphically depicts the velocity profile of the molten glass throughthe flow control region 144 and annular flow channel 142 of the firstouter cylindrical container 130. In FIG. 9A, the velocity of the moltenglass increases from dark gray to light gray. As indicated by FIG. 9A,the velocity of the molten glass remains generally constant through theflow control region 144 and annular flow channel 142 until the moltenglass reaches the delivery ring 136. FIG. 9B graphically depicts thepressure profile of the molten glass in the flow control region 144 andthe annular flow channel 142 of the first outer cylindrical container130. In FIG. 9B, the pressure increases from dark gray to light gray sothat darker gray represents regions of lower pressure and lighter grayrepresents regions of higher pressure. As shown in FIG. 9B, the pressureis greatest at the beginning of the flow control region 144 where themolten glass enters the gap G2 defined between the flow control valve170 and the first outer cylindrical container 130 and/or innermostcylindrical container 110. FIG. 10 graphically depicts the mass flowrate of the molten glass through the flow control region 144 as afunction of the position of the flow control valve 170. In FIG. 10, thezero position on the x-axis corresponds to the minimum position of theflow control valve 170. For the geometric design of the apparatus 100 inthe model depicted in FIGS. 9A and 9B, the mass flow rate of moltenglass through the flow control region 144 varies non-linearly relativeto the position of the flow control valve 170, as shown in FIG. 10, andattains a maximum mass flow rate at the maximum open position of theflow control valve 170.

Referring to FIGS. 3A-3C, changing the position of each of theindependently movable flow control valves 170 relative to the firstouter cylindrical container 130 may change the flow rate of molten glassthrough the annular flow channel 142, thereby changing the thickness ofthe glass layer associated with the cylindrical container. For example,all of the independently translatable flow control valves 170 may betranslated in concert to increase or decrease the overall thickness ofthe glass layer associated with the first outer cylindrical container130.

Without the flow control valves 170, the thickness of the glass layerproduced from each of the cylindrical containers 102 may be adjusted bycontrolling the level of molten glass in each of the cylindricalcontainers 102 or by controlling the viscosity of the molten glass ineach of the cylindrical containers 102. However, these methods ofcontrolling the circumferential thickness distribution of the glasslayers by controlling the level of glass in the cylindrical container102 or controlling the viscosity of the glass may be limiting andimpractical. For example, to accommodate a broad range of glass layerthicknesses, the cylindrical containers 102 must have a large range ofoperating glass levels to achieve the desirable range of net flow ratesfor each glass layer. With an undefined glass line (i.e., variable levelof glass), the design and operation of the apparatus may be impracticalin that it may be difficult to define heating zones for the gaseousatmosphere above the molten glass and for the glass below. It is also asignificant challenge to independently control the viscosity for each ofthe glass layers, especially towards the bottom of the cylindricalcontainers 102, where the glass streams are so close to each other andthe tendency would be for the glass layers to have similar temperatures.

By including flow control valves 170 to control the flow rate of moltenglass, the apparatus 100 provides for adjusting the thickness of eachglass layer while maintaining the same glass level in the cylindricalcontainer 102, such as the first outer cylindrical container 130. Thus,the apparatus 100 that includes the flow control valves 170 allows forsimpler design of heating systems for heating the gaseous space abovethe molten glass as well as the outer surfaces of the cylindricalcontainers 102 compared to controlling the thickness by changing thelevel or viscosity of the molten glass. Additionally, the flow controlvalves 170 may provide a faster control response time compared tochanging the level or viscosity of the molten glass in the cylindricalcontainers 102 due to the control response of the flow control valves170 being mechanical rather than thermal.

Additionally, each of the flow control valves 170 may be independentlytranslatable relative to each of the other flow control valves 170associated with the first outer cylindrical container 130 to modify thecircumferential flow distribution of the molten glass through the flowcontrol region 144 and the annular flow channel 142, thereby modifyingthe circumferential thickness distribution for the glass layerassociated with the first outer cylindrical container 130. For example,in some embodiments, the relative positions of the flow control valves170 within the first outer cylindrical container 130 may be adjusted tocompensate for the differences in glass level in the first outercylindrical container 130 due to the single feed tube 118 and thecircumferential flow of the molten glass from the angular sector 184associated with the feed tube 118 to each of the other angular sectorsof the first outer cylindrical container 130. Additionally, in otherembodiments, one or a plurality of flow control valves 170 of the firstouter cylindrical container 130 may be independently translatablerelative to the other flow control valves 170 to modify the siding ofthe glass layer 214 and/or the composite glass tube 200.

The shape of the flow control region 144 may influence the sensitivityof the apparatus 100 to changes in the position of the flow controlvalves relative to the cylindrical containers. In particular, changes inthe shape of the flow control region 144 may influence the sensitivityof the response in the change of the flow rate of molten glass throughthe flow control region 144 to changes in the position of the flowcontrol valve 170 relative to the flow control region 144. For example,referring to FIGS. 4A-4C, the inner surface 134 of the side wall 132 andthe outer surface 115 of the side wall 112 may slope gradually towardseach other in the flow control region 144. The slope of each of theinner surface 134 of the side wall 132 and the outer surface 115 of theside wall 112 may influence the sensitivity of the apparatus to changesin the position of the flow control valves 170 relative to the flowcontrol region 144. For example, a flow control region 144 with agreater slope may result in decreased sensitivity, because a unit changein the vertical position of the flow control valve 170 results in lessof a change in the cross-sectional area of the channel formed betweenthe flow control valve 170 and the side wall 132 and side wall 112compared to a flow control region 144 having a lesser slope. The shapeof the flow control region 144 may also be limited by otherconsiderations, such as desired throughput for example.

The apparatus 100 may be less sensitive to deviations in the +/−r and+/−θ positions of shafts 174 of the flow control valves 170 compared tothe blow tube 120 disposed within the innermost cylindrical container110 or compared to translation of the first outer cylindrical container130 relative to the innermost cylindrical container 110. For the blowtube 120, deviations in the +/−r or +/−θ position of the blow tube 120may directly impact the circumferential flow distribution of the moltenglass as well as producing a second order change on the flow rate ofmolten glass between the head 122 and the side wall 112 of the innermostcylindrical container 110. Likewise, translation of the first outercylindrical container 130 relative to the innermost cylindricalcontainer 110 may also directly impact the circumferential flowdistribution of the molten glass and may produce the second order changeon the overall flow rate of the molten glass. In contrast, the flowcontrol valves 170 associated with the first outer cylindrical container130 may be translated in the +/−Z direction to change both the net flowrate and the circumferential flow distribution. Thus, deviations in the+/−r or +/−θ position of the shaft 174 of an individual one of the flowcontrol valves 170 does not have a direct impact on the circumferentialflow distribution, but only the smaller, second-order influence on thenew flow rate of the molten glass. Therefore, the flow control valves170 are less sensitive to changes in the +/−r or +/−θ position of theshafts 174 of the flow control valves 170 compared to changes in the+/−r or +/−θ positions of the blow tube 120.

Although described in the context of the first outer cylindricalcontainer 130, it is understood that operation of additional cylindricalcontainers 102, such as second outer cylindrical container 150, toproduce additional glass layers may be similar to that described abovefor operation of the first outer cylindrical container 130.

Referring to FIG. 7A, a molten glass composition 202 may be introducedto the innermost cylindrical container 110, and inner glass layer 212comprising the molten glass composition 202 may be produced at thedistal end 117 of the innermost delivery ring 116. Operation of theinnermost cylindrical container 110 and blow tube 120 to produce theinner glass layer 212 was previously described in relation to theinnermost cylindrical container 110. Another molten glass composition204 may be introduced to the annular chamber 140 of the first outercylindrical container 130, and the middle glass layer 214 comprising themolten glass composition 204 may be produced at the distal end 137 ofthe first outer delivery ring 136, as previously described.Additionally, still another molten glass composition 206 may beintroduced to the annular chamber 160 of the second outer cylindricalcontainer 150, and an outer glass layer 216 comprising the molten glasscomposition 206 may be produced at the distal end 157 of the secondouter delivery ring 156. The molten glass composition 202, the moltenglass composition 204, and the molten glass composition 206 may be thesame or different glass compositions.

The inner glass layer 212, the middle glass layer 214, and the outerglass layer 216 may converge downstream of the distal ends 117, 137, 157of the delivery rings 116, 136, 156 to form the composite glass tube200. In particular, when the molten glass composition 202 reaches thebottom of the head 122 of the blow tube 120, the inner surface of theinner glass layer 212 transitions from being bound by a solid wall intoa free surface. The inner glass layer 212 may continue to flow downwards(i.e., in the −Z direction of the coordinate axis of FIG. 7A) whilemaintaining contact with the innermost delivery ring 116. At the distalend 117 of the innermost delivery ring 116, the inner glass layer 212may separate from the innermost delivery ring 116 and merge with themiddle glass layer 214 to form a first composite stream. The firstcomposite stream that includes the inner glass layer 212 and the middleglass layer 214 may continue to flow downward along the first outerdelivery ring 136 with the middle glass layer 214 in contact with thefirst outer delivery ring 136. At the distal end 137 of the first outerdelivery ring 136, the middle glass layer 214 may separate from thefirst outer delivery ring 136, and the first composite stream may mergewith the outer glass layer 216 to form a second composite glass streamthat includes the inner glass layer 212, the middle glass layer 214, andthe outer glass layer 216. The second composite glass stream, still in amolten or partially molten state, may continue to flow verticallydownward along the second outer delivery ring 156 with the outer glasslayer 216 in contact with the second outer delivery ring 156. At thedistal end 157 of the second outer delivery ring 156, the outer glasslayer 216 may separate from the second outer delivery ring 156 to formthe glass catenary or vertical draw that eventually becomes thecomposite glass tube 200 that includes the plurality of glass layers.Gas flow delivered by the blow tube 120 may determine an inner diameterof the inner glass layer 212 as the glass layers 212, 214, 216sequentially separate from their respective delivery rings 116, 136,156. After separation from the second outer delivery ring 156, thecomposite glass tube 200 may continue to travel downward from theapparatus 100, where the composite glass tube 200 may cool to form asolid composite glass tube that includes a plurality of glass layers.

Operation of the apparatus 100 to form a composite glass tube 200 hasbeen described in the context of producing a composite glass tube 200having three glass layers: the inner glass layer 212, the middle glasslayer 214, and the outer glass layer 216. However, it is understood thatthe apparatus 100 may be configured to produce composite glass tubes 200with more or less glass layers. For example, in some embodiments, thecomposite glass tube 200 may include only a single layer. In otherembodiments, the composite glass tube 200 may have two glass layers: aninner glass layer 212 and an outer glass layer 216. In still otherembodiments, the composite glass tube 200 may have more than three glasslayers, which may include a plurality of inner layers 212, a pluralityof middle glass layers 214, and/or a plurality of outer glass layers216. The glass compositions of each glass layer may be the same ordifferent.

Referring to FIGS. 4A-4C, each of the flow control valves 170 mayinclude a positioner 178 operable to independently position each of theflow control vavles 170 relative to the first outer cylindricalcontainer 130 or other cylindrical container 102. In some embodiments,the positioner 178 for each of the flow control valves 170 may have asingle degree of freedom. For example, as shown in FIG. 4A, thepositioner 178 may translate the flow control valve 170 in the +/−Zdirection of the coordinate axis in FIG. 4A. Referring to FIG. 8, thepositioner 178 may include a plurality of linear positioning stages 179.In some embodiments, the positioner may be a manual positioner.Alternatively, in other embodiments, the positioner 178 may include anautomatic positioner. In some embodiments, the automatic positioners mayinclude motorized linear stages, for example. The simple mechanisms ofthe flow control valve 170 and positioner 178 may enable replacement orrepair of the main components of the flow control valve 170 orpositioner 178 without substantial delays in tubing production.

Referring to FIGS. 7A through 7D, various embodiments of the innermostcylindrical container 110 will now be described. As shown in FIG. 7A anddescribed previously, the innermost cylindrical container 110 may havethe blow tube 120 with the bell-shaped head 122 at the proximal end 121of the blow tube 120. As previously described, the circumferentialdistribution and thickness of the inner glass layer 212 produced fromthe innermost cylindrical container 110 may be controlled by modifyingthe position of the blow tube 120 relative to the central opening 129 ofthe innermost cylindrical container 110. The blow tube 120 may betranslated vertically (i.e., in the +/−Z direction of the coordinateaxis of FIG. 7A) to change the gap G1 between the bell shaped head 122of the blow tube 120 and the inner surface 114 of the innermostcylindrical container 110. Modifying the gap G1 by translation of theblow tube 120 in the vertical direction may change the flow rate of themolten glass composition 202 through the gap G1, thereby changing thethickness of the inner glass layer 212 produced from the innermostcylindrical container 110. Additionally, the blow tube 120 may betranslated horizontally (i.e., in the +/−r or +/−θ directions of thecylindrical coordinate axis of FIG. 7A) relative to the innermostcylindrical container 110 to change the circumferential distribution ofthe molten glass composition 202 flowing between the bell-shaped head122 of the blow tube 120 and the innermost cylindrical container 110,thereby modifying the circumferential thickness distribution of theinner glass layer 212 produced by the innermost cylindrical container110.

Referring to FIG. 7A, the delivery rings 116, 136, 156 may be arrangedso that the distal end 137 of the first outer delivery ring 136 ispositioned vertically below the distal end 117 of the innermost deliveryring 116 and the distal end 157 of the second outer delivery ring 156 ispositioned vertically below the distal end 137 of the first outerdelivery ring 136. In this configuration depicted in FIG. 7A, the innerglass layer 212 may separate from the distal end 117 of the innermostdelivery ring 116 and merge with the middle glass layer 214 to form thefirst composite stream. The first composite stream that includes theinner glass layer 212 and the middle glass layer 214 may then separatefrom the distal end 137 of the first outer delivery ring 136 and mergewith the outer glass layer 216 to form the second composite glassstream. The second composite glass stream, which may still be in amolten or partially molten state, may then be separated from the distalend 157 of the second outer delivery ring 156 to form the glass catenaryor vertical draw, which eventually becomes the composite glass tube 200that includes the plurality of glass layers. Although the apparatus ofFIG. 7A is described in the context of producing a composite glass tube200 having three glass layers, additional glass layers may be added tothe composite glass tube 200 by including additional cylindricalcontainers 102 without substantially changing the principles ofoperation of the apparatus 100 in FIG. 7A.

Referring now to FIG. 7B, in some embodiments, the blow tube 120 mayextend through the central opening 129 in the bottom wall 113 of theinnermost cylindrical container 110 and through the inner delivery ring116. In this embodiment, the bell-shaped head 122 on the proximal end121 of the blow tube 120 may be positioned vertically below (i.e., inthe −Z direction of the coordinate axis of FIG. 7B) the distal end 117of the inner delivery ring 116. Gap G3 may be defined between the head122 of the blow tube 120 and the distal end 117 of the inner deliveryring 116. Translation of the blow tube 120 in the vertical direction(i.e., in the +/−Z direction of the coordinate axis of FIG. 7B) maychange the width of the gap G3, thereby changing the impedance to flowof molten glass composition 202 through the gap G3, which may increaseor decrease the flow rate of the molten glass composition 202. Forexample, in the embodiment depicted in FIG. 7B, translating the blowtube 120 vertically downward may increase the width of the gap G3,thereby increasing the flow rate of the molten glass composition 202through the gap G3. Conversely, translating the blow tube of FIG. 7B inthe vertically upward direction (i.e., the +Z direction of thecoordinate axis of FIG. 7B) may decrease the width of the gap G3,thereby decreasing the flow rate of the molten glass composition 202through the gap G3. In other embodiments, the head 122 of the blow tube120 or the distal end 117 of the inner delivery ring 116 may be shapedso that translation of the blow tube 120 in the +Z direction of thecoordinate axis of FIG. 7B may increase the width of the gap G3 andthereby increase the flow rate of the molten glass composition 202therethrough.

As also shown in FIG. 7B, in some embodiments, the inner delivery ring116 may extend vertically downward farther than the other delivery rings136, 156, with each successively outwardly positioned delivery ring 136,156 becoming shorter in the vertical dimension (i.e., the +/−Z directionof the coordinate axis of FIG. 7B). In this configuration, the distalend 137 of the first outer delivery ring 136 may be positionedvertically below (i.e., in the −Z direction) the distal end 157 of thesecond outer delivery ring 156, and the distal end 117 of the innermostdelivery ring 116 may be positioned vertically below the distal end 137of the first outer delivery ring 136. In the embodiments represented byFIG. 7B, the outer glass layer 216 may be the glass layer that detachesfirst from the second outer delivery ring 156. The outer glass layer 216may separate from the distal end 157 of the second outer delivery ring156. After separation from the second outer delivery ring 156, the outerglass layer 216 may be bounded on one side by the outer surface of thefirst outer delivery ring 136. At the distal end 137 of the first outerdelivery ring 136, the outer glass layer 216 and the middle glass layer214 may separate from the first outer delivery ring 136 and mergetogether to produce a first composite stream that includes the middleglass layer 214 and the outer glass layer 216. The first compositestream that includes the middle glass layer 214 and the outer glasslayer 216 may remain bounded by the outer surface of the innermostdelivery ring 116. At the distal end 117 of the innermost delivery ring116, the middle glass layer 216 of the first composite stream and theinner glass layer 212 may separate or detach from the innermost deliveryring 116 and merge together to produce the second composite glassstream. The second composite glass stream that includes the inner glasslayer 212, the middle glass layer 214, and the outer glass layer 216,which may still be in a molten or partially molten state, may continueto flow downward along the head 122 of the blow tube 120 until thesecond composite glass stream separates from the proximal end 121 of theblow tube 120, where the second composite glass stream forms the glasscatenary or vertical draw that becomes the composite glass tube 200. Gasflow delivered from the proximal end 121 of the blow tube 120 maydetermine an inner dimension (e.g., diameter) of the inner glass layer212 as the second composite glass stream separates from the proximal end121 of the blow tube 120. After separation from the proximal end 121 ofthe blow tube 120, the composite glass tube 200 may continue to traveldownward from the apparatus 100, where the composite glass tube 200 maycool to form a solid composite glass tube that includes the plurality ofglass layers. Although the apparatus 100 in FIG. 7B is described in thecontext of producing a composite glass tube 200 having three glasslayers, additional glass layers may be added to the composite glass tube200 by including additional cylindrical containers 102 withoutsubstantially changing the principles of operation of the apparatus 100in FIG. 7B.

Referring to FIG. 7C, in some embodiments, the innermost cylindricalcontainer 110 may include at least one inner flow control valve 190. Theinner flow control valve 190 may include a control element 192 that maybe coupled to a shaft 194. The control element 192 may be shaped to forma gap G4 between a control surface 196 of the control element 192 andthe inner surface 114 of the innermost cylindrical container 110. Thecontrol element 192 of the inner flow control valve 190 may have any ofthe features previously described for the control element 172 of theflow control valve 170. In some embodiments, the innermost cylindricalcontainer 110 may include a single inner flow control valve 190. Thecontrol element 192 of the inner flow control valve 190 may be annularin shape so that the control element 192 circumscribes a portion of theblow tube 120. The control surface 196 of the control element 192 may beshaped to conform to the shape of the inner surface 114 of the innermostcylindrical container 110. For example, the control surface 196 of thecontrol element 192 may mirror the shape of the inner surface 114 of theinnermost cylindrical container 110. In some embodiments, the controlsurface 196 may slope downward and inward (i.e., in the −Z anddecreasing r directions of the coordinate axis of FIG. 7C) from an upperportion of the control element 192 to the lower portion of the controlelement 192.

The shaft 194 of the inner flow control valve 190 may have any of thepreviously described features of the shaft 174 of the flow control valve170. As shown in FIG. 7C, the blow tube 120 may extend downward throughthe innermost delivery ring 116 so that the head 122 of the blow tube120 is positioned vertically below the distal end 117 of the innermostdelivery ring 116. In some embodiments, the shaft 194 of the inner flowcontrol valve 190 may be a hollow cylindrical tube that circumscribes atleast a portion of the blow tube 120. The inner flow control valve 190may be translatable in the vertical direction (i.e., the +/−Z directionof the coordinate axis of FIG. 7C) relative to the innermost cylindricalcontainer 110. In some embodiments, the inner flow control valve 190 maybe vertically translatable relative to the blow tube 120. For example,in some embodiments, the blow tube 120 may be fixed in the verticaldirection (i.e., in the +/−Z direction of the coordinate axis of FIG.7C) and the inner flow control valve 190 may be translatable in thevertical direction relative to the blow tube 120. Vertical translationof the inner flow control valve 190 may change width of the gap G4,which may change the net flow rate of the molten glass composition 202from the innermost cylindrical container 110 to the inner delivery ring116, thereby changing the average thickness of the inner glass layer 212associated with the innermost cylindrical container 110.

In some embodiments, the blow tube 120 may also be translatable in thevertical direction (i.e., the +/−Z direction). Vertical translation ofthe blow tube 120 may be independent of vertical translation of theinner flow control valve 190. Translation of the blow tube 120 in thevertical direction may enable adjustment of the glass delivery viscosityat the head 122 of the blow tube 120 without changing the net flow rateof the molten glass composition 202 from the innermost cylindricalcontainer 110. Adjusting the glass delivery viscosity may enablemodification of the catenary shape, landing temperature, and/or thepressure of the blow air required.

In some embodiments, the inner flow control valve 190 may betranslatable with the blow tube 120 in the radial and/or angulardirections (i.e., in the +/−r and/or the +/−θ directions of thecoordinate axis of FIG. 7C). Translation of the blow tube 120 and theinner flow control valve 190 together in the radial and/or angulardirections may determine the circumferential flow rate distribution ofthe molten glass composition 202 from the innermost cylindricalcontainer 110. Translating the blow tube 120 and inner flow controlvalve 190 of FIG. 7C in the radial and angular direction to change thecircumferential flow rate distribution of the molten glass composition202 may enable modification of the circumferential thickness profile ofthe inner glass layer 212 associated with the innermost cylindricalcontainer 110. Additionally, modifying the circumferential flow ratedistribution of the molten glass composition 202 by translating the blowtube 120 and inner flow control valve 190 in the radial and angulardirections may compensate for single point continuous feed of the moltenglass composition 202 from the feed tube 118 (FIG. 1A) to the innermostcylindrical container 110. Alternatively, the inner flow control valve190 may be translatable in the radial and/or angular directions (i.e.,in the +/−r and/or the +/−θ directions of the coordinate axis of FIG.7C) independent of the blow tube 120.

Alternatively, in other embodiments, the innermost cylindrical container110 may have a plurality of inner flow control valves 190. In theseembodiments, the blow tube 120 may be fixed in the vertical, radial, andangular directions and the circumferential flow rate distribution of themolten glass composition 202 may be controlled by translation of each ofthe inner flow control valves 190 relative to the innermost cylindricalcontainer 110 and each of the other of the plurality of the inner flowcontrol valves 190.

In the embodiments represented by FIG. 7C, the delivery rings have thesame configuration as shown in FIG. 7B. Thus, the separation of eachglass layer 212, 214, 216 from the associated delivery ring 116, 136,156 and confluence of the glass layers 212, 216, 216 to form thecomposite glass tube 200 is the same as previously described in relationto FIG. 7B.

Referring to FIG. 7D, in still other embodiments, the innermostcylindrical container 110 may include at least one of the inner flowcontrol valves 190 illustrated in FIG. 7C and described with referencethereto. However, the embodiment in FIG. 7D differs from the embodimentof FIG. 7C in the configuration of the delivery rings 116, 136, 156 andthe confluence of the different glass layers to form the composite glasstube 200. In the embodiments represented in FIG. 7D, the proximal end121 of the blow tube 120 may extend through the innermost delivery ring116 so that the head 122 of the blow tube 120 is positioned verticallybelow (i.e., in the −Z direction of the coordinate axis in FIG. 7D) thedistal end 117 of the innermost delivery ring 116. In FIG. 7D, the firstouter delivery ring 136 extends vertically downward so that the distalend 137 of the first outer delivery ring 136 is positioned verticallybelow the distal end 117 of the first outer delivery ring 136, and thesecond outer delivery ring 156 extends vertically downward so that thedistal end 157 of the second outer delivery ring 156 is positionedvertically below the distal end 137 of the first outer delivery ring136. The configuration of the delivery rings 116, 136, 156 in FIG. 7Dare similar to the configuration of the delivery rings 116, 136, 156illustrated in FIG. 7A and described in relation thereto.

Referring to FIG. 7D, in operation, the inner glass layer 212 mayseparate from the innermost delivery ring 116 and merge with the middleglass layer 214 to form a first composite stream that includes the innerglass layer 212 and the middle glass layer 214. At the point where theinner glass layer 212 merges with the middle glass layer 214, the innerglass layer 212 may be solid wall bounded by the blow tube 120 on theside opposite the middle glass layer 214, and the middle glass layer 214may be solid wall bounded by the first outer delivery ring 136 on theside of the middle glass layer 214 opposite the inner glass layer 212.The first composite stream that includes the inner glass layer 212 andthe middle glass layer 214 may continue to flow vertically downward(i.e., in the −Z direction) while attached to the first outer deliveryring 136 and the blow tube 120. At the distal end 137 of the first outerdelivery ring 136, the middle glass layer 214 of the first compositestream may separate from the first outer delivery ring 136 and may thenmerge with the outer glass layer 216 to form a second composite glassstream. At the point where the first composite stream merges with theouter glass layer 216, the inner glass layer 212 of the first compositestream may continue to be solid wall bound by the blow tube 120, and theouter glass layer 216 may be solid wall bound by the second outerdelivery ring 156. The second composite glass stream that includes theinner glass layer 212, the middle glass layer 214, and the outer glasslayer 216, may continue to flow vertically downward while attached tothe second outer delivery ring 156 and the blow tube 120. At the distalend 157 of the second outer delivery ring 156, the outer glass layer 216of the second composite glass stream may detach or separate from thesecond outer delivery ring 156 to form a free surface at the outersurface of the outer glass layer 216. The second composite glass streamthat includes the inner glass layer 212, the middle glass layer 214, andthe outer glass layer 216, which may still be in a molten or partiallymolten state, may continue to flow vertically downward along the head122 of the blow tube 120. The second composite glass stream may separatefrom the proximal end 121 of the blow tube 120, where the secondcomposite glass stream forms the glass catenary or vertical draw thateventually becomes the composite glass tube 200. Gas flow delivered fromthe proximal end 121 of the blow tube 120 may determine an innerdimension (e.g., diameter) of the inner glass layer 212 as the secondcomposite glass stream separates from the proximal end 121 of the blowtube 120. After separation from the proximal end 121 of the blow tube120, the composite glass tube 200 may continue to travel downward fromthe apparatus 100, where the composite glass tube 200 may cool to form asolid composite glass tube 200 that includes the plurality of glasslayers.

Although the apparatus 100 in FIG. 7D is described in the context ofproducing a composite glass tube having three glass layers, additionalglass layers may be added to the composite glass tube by includingadditional cylindrical containers without substantially changing theprinciples of operation of the apparatus 100 in FIG. 7B.

Referring to FIG. 8, another embodiment of the apparatus 100 forproducing composite glass tube that includes a plurality of glass layersis depicted. The apparatus 100 depicted in FIG. 8 includes threecylindrical containers 102 arranged concentrically and fixed withrespect to each other. The three cylindrical containers 102 include theinnermost cylindrical container 110, the first outer cylindricalcontainer 130, and the second outer cylindrical container 150. Althoughdepicted as including 3 cylindrical containers 102, it is understoodthat the apparatus 100 could have more than 3 or less than 3 cylindricalcontainers 102. A total of 8 flow gussets 182 are positioned between theinnermost cylindrical container 110 and the first outer cylindricalcontainer 130, separating the annular flow channel 142 into 8 angularsectors 184 (see FIG. 6D). A total of 8 flow gussets 182 are positionedbetween the first outer cylindrical container 130 and the second outercylindrical container 150, separating the annular flow channel 162 into8 angular sectors 184. Eight flow control valves 170 are disposedbetween the innermost cylindrical container 110 and the first outercylindrical container 130 and positioned with the control element 172 ofeach flow control valve 170 positioned proximate to the flow controlregion 144 in one of the angular sectors 184. Another 8 flow controlvalves 170 may be disposed between the first outer cylindrical container130 and the second outer cylindrical container 150 and positionedrelative to each of the angular sectors 184.

Referring to FIG. 8, the apparatus 100 may additionally include arefractory assembly 300. The refractory assembly 300 may surround theplurality of cylindrical containers 102. The refractory assembly 300 mayalso support the plurality of cylindrical containers 102. The refractoryassembly 300 may include one or more insulating layers 302 comprising arefractory material. The refractory material may be refractory ceramicmaterials that are chemically compatible with the molten glass andcapable of withstanding the high temperatures associated with the glasstube forming process. Typical ceramic refractory materials from whichthe insulating layers 302 can be formed include, without limitation,zircon (e.g., zirconia), silicon carbide, xenotime, alumina basedrefractory ceramics, and/or aluminosilicate refractory ceramics. Theinsulating layers 302 may completely surround the plurality ofcylindrical containers 102. In some embodiments, the refractory assembly300, in particular the insulating layers 302 of the refractory assembly300, may define an orifice 303 positioned vertically below (i.e., in the−Z direction of the coordinate axis of FIG. 8) the delivery rings of theplurality of cylindrical containers 102. The insulating layers 302 maybe operable to reduce heat transfer away from the cylindrical containers102.

In some embodiments, the refractory assembly 300 may include one or aplurality of heating elements 304 embedded in the refractory material ofthe insulating layers 302. The heating element 304 may includeelectrical heating elements, such as platinum windings circumscribingthe plurality of cylindrical containers 102, as shown in FIG. 8. In someembodiments, heating may be provided to the cylindrical containers 102by an induction heating system. Other heating elements 304 arecontemplated for heating the cylindrical containers 102. The combinationof the heating elements 304 and insulating layers 302 may enable controlthe temperatures around and outside the plurality of cylindricalcontainers 102, such as at an outer surface of the second outercylindrical container 150. The refractory assembly 300 may additionallyinclude a cover block 306 positioned on top of the plurality ofcylindrical containers 102 and/or the insulating layers 302 of therefractory assembly 300.

The apparatus 100 may also include an internal heating system 310 forheating the gaseous space above the molten glass disposed in thecylindrical containers 102. In some embodiments, the internal heatingsystem 310 may include internal heating elements 312 positioned insideof the refractory assembly 300, such as between the cover block 306 andthe plurality of cylindrical containers 102. The internal heatingelements 312 may be positioned to heat the gaseous space above themolten glass in each of the cylindrical containers 102. The internalheating elements 312 may include, but are not limited to, burners,radiant heaters such as platinum windings, or other type of heatingelements or systems. In some embodiments, the internal heating system310 may include an inductive heating system. The internal heating system310 may provide heat to the annular chambers to maintain the glasscompositions in the molten state.

Referring to FIG. 8, in some embodiments, the apparatus 100 may includea support structure 320 positioned above the refractory assembly 300,such as above the cover block 306. The support structure 320 may providesupport for the positioners 178 for the plurality of flow control valves170. As shown in FIG. 8 and previously described, the positioners 178may include a plurality of vertical positioning stages 179 that enabletranslation of each of the flow control valves 170 relative to thestationary cylindrical containers 102.

Referring to FIG. 11, a system 400 for producing a composite glass tube200 that includes a plurality of glass layers is illustrated. The system400 may include the apparatus 100, a control system 402, and a sensor410. The apparatus 100 may have any of the features previously describedherein. In particular, the apparatus 100 may include a plurality of theflow control valves 170 and a plurality of the positioners 178, each ofthe positioners 178 operatively coupled to one of the flow controlvalves 170 to translate the flow control valves 170 relative to thecylindrical containers 102 of the apparatus 100. The positioners 178 maybe automated. For example, the positioners 178 may include one or morepositioning motors. Other automatic mechanical, electro-mechanical,pneumatic, hydraulic, or magnetic positioning devices may also beincluded in the positioners 178. Each of the positioners 178 may becommunicatively coupled to the control system 402.

As used herein, the term “communicatively coupled to” includes allpractical forms of communication between components of a control system,such as system 400. These forms of communication may include wiredcommunications, such as communication through electrical or fiber opticcables for example. Wired communications may also include communicationthrough a slip ring for communication between components that rotaterelative to each other. Communication may also include wirelesscommunications, such as communication through radio waves, light,radiation, other wireless communication methods, or combinations ofthese. The control system 402 may be communicatively coupled to any ofthe motors, actuators, control valves, sensors, burners, heatingelements, or other components of the system 400 disclosed herein.

The sensor 410 may be positioned downstream of the apparatus 100. Thesensor 410 may be operable to measure or determine one or moredimensions or properties of the composite glass tube 200 produced by theapparatus. For example, the sensor 410 may be operable to measure theoverall thickness of the composite glass tube 200, the average thicknessof one or more than one glass layer of the composite glass tube 200, thecircumferential thickness profile (i.e., sidings) of the composite glasstube 200, the circumferential thickness profile of one or more than oneof the glass layers of the composite glass tube 200, an inner diameterof the composite glass tube 200 or a specific glass layer, an outerdiameter of the composite glass tube 200 or a specific glass layer, orother dimensions of the composite glass tube. The sensor 410 may includean optical imaging system, laser reflectometer, laser gauge, opticalmicrometer, or other sensor suitable for measuring one or moredimensions of the glass tube. The sensor 410 may be communicativelycoupled to the control system 402.

Referring to FIG. 11, the control system 402 may include a processor404, at least one memory module 406 communicatively coupled to theprocessor 404, and machine readable instructions stored on the at leastone memory module. The control system 402 may also include a display 408and/or an input device 409 communicatively coupled to the processor 404for inputting and outputting information from an operator of the system400. The machine readable instructions may cause the system 400 toperform at least the following when executed by the processor 404:measure a dimension of the composite glass tube 200; compare thedimension of the composite glass tube 200 to a target dimension of thecomposite glass tube 200; and position one or more than one of theplurality of flow control valves 170 to change the dimension of thecomposite glass tube 200 based on the comparison. In some embodiments,the memory module 406 may include a database and/or stored data thatincludes information on the target dimensions and/or target propertiesof the composite glass tube 200. In some embodiments, the machinereadable instructions, when executed by the processor 404, may cause thecontrol system 402 to receive or retrieve a measured dimension and/or ameasured property of the composite glass tube 200 from the sensor 410,compare the measured dimension and/or measured property received orretrieved from the sensor 410 to the target dimension or target propertystored on the memory module 406, calculate one or a plurality of controlresponses based on the comparison of the measured dimension or measuredproperty with the target dimension or target property, and send thecontrol responses to the plurality of positioners 178.

Referring to FIG. 11, in some embodiments, the apparatus 100 may includea blow tube positioner 414 operatively coupled to the blow tube 120disposed in the innermost cylindrical container 110 of the apparatus100. The blow tube positioner 414 may be operable to translate the blowtube relative to the innermost cylindrical container 110 to control thethickness of the innermost glass layer (i.e., inner glass layer 212 ofFIG. 7A) or the circumferential thickness profile of the innermost glasslayer. The control system 402 may be communicatively coupled to the blowtube positioner 414. The system 400 may include machine readableinstructions stored in the memory modules 406 that, when executed by theprocessor 404, may cause the system 400 to measure a dimension of theinnermost glass layer of the composite glass tube 200, compare themeasured dimension of the innermost glass layer of the composite glasstube 200 to a target dimension of the innermost glass layer, andposition the blow tube 120 relative to the innermost cylindricalcontainer 110 (FIG. 1A) to change the dimension of the innermost glasslayer of the composite glass tube 200 based on the comparison. Thetarget dimension may be stored in the memory module 406.

In some embodiments, the measured dimension may be an average thicknessof the innermost layer and the machine readable instructions stored inthe one or more memory modules 406, when executed by the processor 404,may cause the system 400 to vertically position the blow tube 120relative to the innermost cylindrical container 110. To verticallyposition the blow tube 120, the system 400 may send a control signal tothe blow tube positioner 414 operatively coupled to the blow tube 120.The control signal may cause the blow tube positioner 414 to translatethe blow tube 120 in the vertical, radial, or angular dimensionsrelative to the innermost cylindrical container 110.

Referring to FIG. 11, in some embodiments, the blow tube 120 may befluidly coupled to a gas system comprising a gas source 416 and a gascontrol valve 418. The gas control valve 418 may be operable to changethe flow rate of a gas through the blow tube 120. The gas control valve418 may be communicatively coupled to the control system 402. Machinereadable instructions stored on the memory modules 406, when executed bythe processor 404, may cause the system 400 to receive a measureddimension of the composite glass tube 200, such as an inner diameter;compare the measured dimension of the composite glass tube 200 against atarget dimension; and change the flow rate of gas through the blow tube120 by sending a control signal to the gas control valve 418 to causethe gas control valve 418 to open or close.

Referring to FIG. 11, the system 400 may also include one or a pluralityof molten glass feed valves 420. Each molten glass feed valve 420 may bedisposed in one of the feed tubes 118 extending from a molten glasssystem 424 to one of the cylindrical containers 102. The molten glasssystem 424 may be any system known in the art for producing a moltenglass composition from raw material components. Although the system 400is shown in FIG. 11 as including a single molten glass feed valve 420and a single molten glass system 424, it is understood that a system 400comprising an apparatus 100 with multiple cylindrical containers 102 mayhave a plurality of molten glass systems 424, each with a feed tube 118and a molten glass feed valve 420. In some embodiments, the molten glassfeed valve 420 may be operatively coupled to an actuator 422 which maybe operable to position the molten glass feed valve 420. The actuator422 may be communicatively coupled to the control system 402. Machinereadable instructions stored on the memory modules 406, when executed bythe processor 404, may cause the system 400 to change the flow rate ofmolten glass into one or more of the cylindrical containers 102 bysending a control signal to the actuator 422 to change the position ofthe molten glass feed valve 420.

Referring to FIGS. 1A-1C and 7A, a method of producing a composite glasstube 200 comprising a plurality of glass layers may include introducinga first molten glass composition to the apparatus 100. The apparatus 100may have any of the previously described features of apparatus 100. Thefirst molten glass composition may be introduced to a first annularchamber (i.e., annular chamber 140) defined between the innermostcylindrical container 110 and the first outer cylindrical container 130.The method may further include introducing a second molten glasscomposition to a second annular chamber (i.e., annular chamber 160)defined between the first outer cylindrical container 130 and the secondouter cylindrical container 150 or to the inner annular chamber 124defined by the innermost cylindrical container 110. The method includespassing the first molten glass composition through a first annular flowchannel to a first outer delivery ring 136 to produce a first annularglass layer, passing the second glass composition through a secondannular flow channel to the second outer delivery ring 156 or to theinnermost delivery ring 116 to produce a second annular glass layer, andcontacting and/or merging the first annular glass layer and the secondannular glass layer to produce the composite glass tube 200. The methodmay further include adjusting an average thickness or a circumferentialthickness profile of at least one of the composite glass tube 200, thefirst annular glass layer, or the second annular glass layer bytranslating at least one of the plurality of flow control valvesrelative to the plurality of cylindrical containers.

In some embodiments, the method may include determining an innerdiameter of the composite glass tube 200 by introducing a flow of a gasto an internal volume of the composite glass tube 200 from the proximalend 121 of the blow tube 120. In some embodiments, the first moltenglass composition has a coefficient of thermal expansion (CTE) differentthan the second molten glass composition. In some embodiments, the firstmolten glass composition may have a Young's modulus that is differentthan the Young's modulus of the second molten glass composition.

In some embodiments, the method may include introducing a third moltenglass composition to one of the second annular chamber 160, a thirdannular chamber defined between the second outer cylindrical container150 and a third outer cylindrical container (see FIG. 2), or theinnermost cylindrical container 110. The method may further includepassing the third glass composition through the second annular flowchannel to the second outer delivery ring 156, through a third annularflow channel to a third outer delivery ring, or to the innermostdelivery ring 116 to produce a third annular glass layer and contactingor merging the third annular glass layer with the first annular glasslayer or the second annular glass layer to produce the composite glasstube 200. The method may further include adjusting an average thicknessor a circumferential thickness profile of the third annular glass layerby translating at least one of the plurality of flow control valves 170relative to the plurality of cylindrical containers 102, such as thefirst outer cylindrical container 130, second outer cylindricalcontainer 150, or other cylindrical container.

In some embodiments, the second molten glass composition may beintroduced to the innermost cylindrical container 110 and the method mayfurther include introducing a third molten glass composition to thesecond annular chamber 160, passing the third glass composition throughthe second annular flow channel 162 to the second outer delivery ring156 to produce a third annular glass layer, and contacting or mergingthe third annular glass layer with the first annular glass layer toproduce the composite glass tube 200, wherein the first annular glasslayer may be disposed between the second annular glass layer and thethird annular glass layer. The first annular glass layer may include aCTE different than the CTE of the second annular glass layer and the CTEof the third annular glass layer. In some embodiments, the method mayinclude adjusting a circumferential distribution of the second moltenglass composition by translating the blow tube 120 in the radialdirection, angular direction, or both relative to the innermostcylindrical container 110. The method may further include adjusting athickness of the second molten glass composition by verticallytranslating the blow tube 120 relative to the innermost cylindricalcontainer 110. In some embodiments, the innermost cylindrical container110 may include the inner flow control valve 190 translatable relativeto the innermost cylindrical container 110 and the method may includeadjusting a thickness of the second annular glass layer by translatingthe inner flow control valve 190 relative to the innermost cylindricalcontainer 110.

The apparatus 100 and/or system 400 (FIG. 11) may be used to produce astrengthened composite glass tube 200 by selecting different glasscompositions for each of the glass layers. In some embodiments, thecomposite glass tube 200 may include at least one middle glass layer(e.g., middle glass layer 214 of FIG. 7A), an inner glass layer (e.g.,inner glass layer 212 of FIG. 7A), and an outer glass layer (e.g., outerglass layer 216 of FIG. 7A). The inner glass layer and the outer glasslayer may be made from glass compositions having properties differentthan the middle glass layers, such as coefficient of thermal expansion(CTE), Young's modulus, or other property. For example, the inner glasslayer and the outer glass layer may be made from glass compositionshaving CTEs that are different than the CTE of the middle glass layer.As the molten glass compositions cool to solidify into the compositeglass tube 200, the difference in the CTE between the glass of themiddle glass layer and the glass of the inner and outer glass layers mayproduce compressive stress in the inner and outer glass layers andtension or tensile stress in the middle glass layer. The composite glasstube 200 is strengthened by the introduction of the compressive stressto the inner and outer glass layers. These compressive stresses mustfirst be overcome before encapsulated flaws in the glass will experienceenough tension to propagate. The apparatus 100 may enable control of thethickness of one or more of the inner glass layer, the outer glasslayer, or the middle glass layer to control the magnitude of thecompressive stress produced in the inner glass layer and outer glasslayer. The apparatus 100 therefore enables strengthening of the glasstube without the need for a secondary tempering process, such as ionexchange or thermal tempering, for example.

In some embodiments, the apparatus 100 and/or system 400 may enablebetter control of cross-sectional shape and thickness of single glass orcomposite glass tubes made from colored glass, such as amber-coloredglass. Colored glasses, in particular amber glass, possess opticalproperties that may be desirable in certain applications, such aspharmaceutical packaging for pharmaceutical compositions that aresensitive to ultraviolet light or other wavelengths of light. It isoften difficult to transfer energy into and through these colored glasscompositions in the molten state. Therefore, the heating systems andheating elements disposed within the apparatus 100 may be insufficientto maintain a uniform temperature of the colored glass compositions inthe cylindrical containers 102. Thus, the molten colored glasscomposition may experience temperature variation in the cylindricalcontainers 102, which may result in oval or oblong cross-sections in theglass tube made from these colored glass compositions.

In conventional glass tube processes, this temperature gradient effectmay be compensated for by using oval or oblong delivery rings or oval oroblong cylindrical containers. However, installing oval or oblongcylindrical containers and delivery rings may render the apparatusunusable for other glass compositions. The apparatus 100 that includesthe plurality of flow control valves 170 for controlling thecircumferential distribution of molten glass during the productionprocess may allow the apparatus 100 and/or system 400 to compensate forthe temperature differences within the cylindrical containers 102without resorting to installing oval or oblong cylindrical containers102 or delivery rings. Thus, the apparatus 100 may enable changingproduction from clear glass tubes to colored-glass tubes and backwithout exchanging any of the components of the apparatus 100.

The composite glass tube 200 produced by the apparatus 100, system 400,and methods described herein may be shaped into glass articles such asbottles, glass containers, etc. The apparatus 100, systems 400, andmethods may be used to produce a physically strengthened composite glasstube 200 by incorporating glass layers with different properties, aspreviously described. The apparatus 100, systems 400, and methods mayalso enable improvements in the chemical durability of the compositeglass tube 200 by using different glass compositions for each of theglass layers. Thus, the composite glass tube 200 made using theapparatus 100, system 400, or methods disclosed herein may beparticularly well suited for use in the formation of pharmaceuticalpackages for containing a pharmaceutical composition, such as liquids,powders and the like, due to the increased strength and chemicaldurability. For example, the composite glass tube 200 made by theapparatus 100, system 400, and/or methods described herein may be usedto form vials, ampoules, cartridges, syringe bodies and/or any otherglass container for storing pharmaceutical compositions.

The present disclosure may be embodied in hardware and/or in software(including firmware, resident software, micro-code, etc.). The system400 (FIG. 11) or the control system 402 may include at least oneprocessor 404 and the computer-readable medium (i.e., memory module 406)as previously described in this specification. A computer-usable or thecomputer-readable medium or memory module may be any medium that cancontain, store, communicate, propagate, or transport the program for useby or in connection with the instruction execution system, apparatus, ordevice.

The computer-usable or computer-readable medium or memory module may be,for example but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium. More specific examples (a non-exhaustive list) ofthe computer-readable medium would include the following: an electricalconnection having one or more wires, a portable computer diskette, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,and a portable compact disc read-only memory (CD-ROM). Note that thecomputer-usable or computer-readable medium could even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory.

Computer program code for carrying out operations of the presentdisclosure may be written in a high-level programming language, such asC or C++, for development convenience. In addition, computer programcode for carrying out operations of the present disclosure may also bewritten in other programming languages, such as, but not limited to,interpreted languages. Some modules or routines may be written inassembly language or even micro-code to enhance performance and/ormemory usage. However, software embodiments of the present disclosure donot depend on implementation with a particular programming language. Itwill be further appreciated that the functionality of any or all of theprogram modules may also be implemented using discrete hardwarecomponents, one or more application specific integrated circuits(ASICs), or a programmed digital signal processor or microcontroller.

EXAMPLES

The following examples illustrate the design and operation of thedisclosed apparatuses 100 for continuously producing composite glasstube that includes a plurality of glass layers. The following propheticexamples were developed in and modeled using commercially availablefluid dynamics model software available from COMSOL.

Example 1

In Example 1, a 3 dimensional (3D) flow model of molten glass throughthe annular space defined between an innermost cylindrical container anda first outer cylindrical container is presented. Referring to FIGS. 1Aand 12, the flow model of Example 1 is based on an apparatus 100 thatincludes the innermost cylindrical container 110 (FIG. 1A) and the firstouter cylindrical container 130 (FIG. 1A). The innermost cylindricalcontainer 110 and the first outer cylindrical container 130 are circularin cross-section and define the annular chamber 140, flow control region144, and the annular flow channel 142 therebetween. The flow controlregion 144 and the annular flow channel 142 are divided into fourequally-sized angular sectors 184 by four flow gussets 182, which areindicated in FIG. 12. The flow gussets 182 cover a vertical distance H(i.e., a distance measured in the +/−Z direction of the coordinate axisof FIG. 12) and separate the angular sectors 184 corresponding to eachof the flow control valves 170. The flow gussets 182 extend downstreamfrom the flow control region 144, through the annular flow channel 142,towards the distal end of the delivery rings 116, 136 (FIG. 1A), andhelp maintain the circumferential flow distribution attained by the flowcontrol valves 170. The model includes the flow control valve 170, inparticular the control element of the flow control valve 170, positionedin the flow control region 144. The model represents one half of thetotal circumference of the innermost cylindrical container 110 and thefirst outer cylindrical container 130 and encompasses portions of threeangular sectors 184 (designated in FIG. 12 as sectors A, B, and C) outof the four equally-sized angular sectors 184 defined by the flowgussets 182. This simplified model assumes symmetry at the 0° and 90°planes, and is sufficient to illustrate some of the important threedimensional flow effects associated with the operation of the apparatus100.

FIGS. 12-14 show the results from the 3D flow model of Example 1 withthe flow control valves 170 for net flow rate and circumferential flowdistribution adjustments. In Example 1, the z-axis position of the flowcontrol valves 170 in angular sectors A and C are lowered down withrespect to the flow control valve 170 in angular sector B. Thus, theflow control valve 170 in angular sector B is in a positioncorresponding to a greater mass flow rate of glass through angularsector B compared to the positions of the flow control valves 170 inangular sectors A and C. FIG. 12 illustrates the distribution of fluidpressure of the molten glass in the annular chamber 140, flow controlregion 144, and annular flow channel 142. For the gray scale for FIG.12, darker gray shades indicate lesser pressure regions, the lightergray shades indicate greater pressure regions, and the pressureincreases from dark gray to light gray. FIG. 13 illustrates the fluidvelocity distribution of the molten glass in the annular chamber 140,flow control region 144, and the annular flow channel 142. In FIG. 13,darker gray shades indicate regions of lesser velocity of the moltenglass, the lighter shades indicate regions of greater velocity of themolten glass, and the velocity of the molten glass increases from darkershades to lighter shades. FIG. 14 illustrates the percent deviation ofthe flow rate of molten glass from the average flow rate of molten glassas a function of angle. As shown in FIGS. 12-14, as the impedance toglass flow is increased, and glass flow through sector B is favored.

Referring to FIG. 12, the fluid pressure in sector B differs from thatof sectors A and C in the region downstream of the flow control valves170. The pressure in angular sector B is greater than the pressure insectors A and C, which indicates a greater flow rate of the molten glassthrough angular sector B. The pressure differential between angularsector B and angular sectors A and C is sustained along the length ofthe flow gussets 182. The flow gussets 182 end at a distance D from thedistal end of the delivery rings. At the end of the flow gussets 182,the glass from each angular sector merges into a single stream, as shownby the normalization of the pressure between angular sector B andangular sectors A and C downstream of the flow gussets 182.

FIG. 13 illustrates the average velocity of the molten glass throughangular sectors A, B, and C in the flow control region 144 and annularflow channel 142. FIG. 13 shows a greater velocity of the molten glassin angular sector B at the end of the flow gussets 182 compared to thevelocity of the molten glass in sectors A and C. This is consistent withthe greater pressure of the molten glass in angular sector B compared tosectors A and C. FIG. 14 illustrates the relative mass flow rate ofmolten glass as a function of the angle through the modeled region.Reference number 1301 indicates the angular positions of the flowgussets in the modeled region. As shown in FIG. 14, the relative flowrate of molten glass attains a maximum 1302 in the angular middle ofangular sector B and decreases as the position moves towards each ofangular sectors A and C. This indicates that positioning the flowcontrol valves 170 for angular sectors A and C vertically down (i.e., −Zdirection) closer to the side wall of the cylindrical containers in theflow control region 144 relative to the position of the flow controlvalve 170 in angular sector B produces preferential flow of molten glassthrough angular sector B over sectors A and C.

FIGS. 15 and 16 illustrate the pressure and flow velocity of the moltenglass in the delivery region of the flow model of Example 1. Thedelivery region in FIGS. 15 and 16 represents the region between theinnermost delivery ring 116 and the first outer delivery ring 136 andfrom the end of the annular flow channel 142 to the distal end of theinnermost delivery ring 116. For the gray scale in FIG. 15, darker grayshades indicate lesser pressure regions, the lighter gray shadesindicate greater pressure regions, and the pressure increases from darkgray to light gray. For the gray scale for FIG. 16, darker gray shadesindicate regions of lesser flow velocity of molten glass, the lightergray shades indicate regions of greater flow velocity of molten glass,and the flow velocity of molten glass increases from dark gray shades tolight gray shades. As shown in FIGS. 15 and 16, the flows of moltenglass from angular sectors A, B, and C confluence at the end of the flowgussets 182 to from a single glass stream. The pressure differencebetween angular sector B and sectors A and C dissipates downstream ofthe end of the flow gussets 182 (i.e., in the −Z direction of thecoordinate axis of FIGS. 15 and 16), and some flow redistribution amongsectors A, B, and C may ensue. The distance D from the end of the flowgussets 182 to the distal end 117 of the innermost delivery ring 116, aswell as the gusset thickness and end profile, may be controlled tocontrol the redistribution of molten glass between sectors and influencethe localized impact of the flow gusset 182 on flow distribution. For agiven geometry of the apparatus, the location of the flow gussets andthe influence on flow distribution may be independent of flow rate andviscosity of the molten glass.

Example 2

In Example 2, a 3 dimensional (3D) flow model of molten glass throughthe annular space defined between an innermost cylindrical container anda first outer cylindrical container is presented. For Example 2, thesame parameters for the apparatus 100 described in Example 1 is usedexcept that the upper portions 1701 of the innermost cylindricalcontainer 110 and the first outer cylindrical container 130 are bothpolygonal in cross-section. Specifically, the innermost cylindricalcontainer 110 and the first outer cylindrical container 130 areoctagonal in cross-section. The flow gussets 182 are positionedproximate to each of the 8 vertices 1702 of the octagonal upper portions1701. The flow control valves 170 extend between each pair of flowgussets 182 and are straight rather than arcuate. The model represents aquarter of the total circumference of the innermost cylindricalcontainer 110 and the first outer cylindrical container 130 andencompasses three angular sectors 184 (designated in FIG. 12 as sectorsA, B, and C) out of the 8 equally-sized angular sectors 184 defined bythe flow gussets 182. This simplified model assumes symmetry at the 0°and 90° planes, and is sufficient to illustrate some of the importantthree dimensional flow effects associated with the operation of theapparatus 100. Example 2 demonstrates that that flow control valves 170do not have to be arcuate in shape to be effective at controlling theflow rate of molten glass through an angular sector.

FIGS. 17 and 18 illustrate the results of the 3D flow model of Example2. As with Example 1, the z-axis position of the flow control valves 170in angular sectors A and C are lowered down with respect to the flowcontrol valve 170 in angular sector B. FIG. 17 illustrates thedistribution of fluid pressure of the molten glass in the annularchamber 140, flow control region 144, and annular flow channel 142. FIG.18 illustrates the fluid velocity distribution of the molten glass inthe annular chamber 140, flow control region 144, and the annular flowchannel 142. For the gray scale in FIG. 17, darker gray shades indicatelesser pressure regions, the lighter gray shades indicate greaterpressure regions, and the pressure increases from dark gray to lightgray. For the gray scale for FIG. 18, darker gray shades indicateregions of lesser flow velocity of molten glass, the lighter gray shadesindicate regions of greater flow velocity of molten glass, and the flowvelocity of molten glass increases from dark gray shades to light grayshades. As shown in FIGS. 17-18, as the impedance to glass flow isincreased in sectors A and C as shown by increasing pressure in the flowcontrol regions 144 in sectors A and C of FIG. 17, the glass flowthrough sector B is favored, as indicated by the increased flow velocityof molten glass through the annular flow channel 142 of sector Bcompared to the flow velocity of molten glass through the annular flowchannels of sectors A and C.

Example 3

In Example 3, the performance and operation of the apparatus including aplurality of cylindrical containers and the flow control valves wasevaluated using an oil model apparatus for controlling the overall flowrate of material through the flow control region 144. FIG. 19illustrates the experimental apparatus 600 used to model operation ofthe flow control valves. The experimental apparatus 600 included twocylindrical containers: the innermost cylindrical container 110 and thefirst outer cylindrical container 130. The innermost cylindricalcontainer 110 and the first outer cylindrical container 130 are circularin cross-section and define the annular chamber 140, flow control region144, and the annular flow channel 142 therebetween. The flow controlregion 144 and the annular flow channel 142 are divided into 4equally-sized angular sectors 184 by 4 flow gussets 182 and each of theangular sectors 184 included a flow control valve 170. The experimentalapparatus 600 can be operated with either one or two oil streams. Theinnermost cylindrical container 110 included a configuration similar tothe configuration depicted in FIG. 7B and previously described inconjunction therewith.

The experimental apparatus 600 was used to validate themulti-cylindrical container apparatus with flow control valves 170 formodifying the net flow rate using the flow control valves. In a firstrun, the four flow control valves 170 were positioned at a first Zposition of 0.5 inches above the minimum operating position. An oilmaterial was introduced to the annular chamber 140 defined between theinnermost cylindrical container 110 and the first outer cylindricalcontainer 130, and the velocity of the free surface of the flowing oildischarged from the outer delivery ring 136 was measured. No oilmaterial was introduced to the innermost cylindrical container 110. In asecond run, the four flow control valves 170 were positioned at a secondZ position of 2 inches above the minimum operating position. The oilmaterial was again introduced to the annular chamber 140 and thevelocity of the free surface of the flowing oil discharged from theouter delivery ring 136 was measured.

Referring to FIG. 20, the velocity of the oil flow (y-axis) at the outerdelivery ring is depicted as a function of the angular position of theouter delivery ring (x-axis) given in degrees. At the Z-position of 0.5inches 1901, the velocity of oil flow at the outer delivery ring 136 wasrelatively constant around the circumference of the outer delivery ring.When the Z-position of the flow control valves increased to 2 inches1902, the average velocity of free surface of the flowing oil at theouter delivery ring 136 increased by about 0.01 inches per second. Thus,changing the Z-position of the flow control valves changes the averageflow velocity, and thereby the average flow rate, of material throughthe apparatus.

Example 4

In Example 4, the performance and operation of the apparatus includingthe plurality of cylindrical containers and flow control valves wasevaluated using the oil model apparatus of FIG. 19 to control thecircumferential distribution of flow of the material from the apparatus.The experimental apparatus 600 used to model operation of the flowcontrol valves is illustrated in FIG. 19 and previously described inExample 3. In a first run of Example 4, a first flow control valve waspositioned at 0.5 inches from the minimum operating position of the flowcontrol valves, and the second, third, and fourth control valves werepositioned at 2 inches from the minimum operating position of the flowcontrol valves. An oil material was introduced to the annular chamber140 and the velocity of the free surface of the flowing oil dischargedfrom the outer delivery ring 136 was measured. In a second run ofExample 4, the first flow control valve was positioned at 1.2 inchesfrom the minimum operating position, and second, third, and fourth flowcontrol valves were again positioned at 2 inches from the minimumoperating position. The oil material was again introduced to the annularchamber 140 and the velocity of the free surface of the flowing oildischarged from the outer delivery ring 136 was measured.

Referring to FIG. 21, the velocity of the free surface of the flowingoil (y-axis) at the outer delivery ring is depicted as a function of theangular position of the outer delivery ring (x-axis) given in degrees.In FIG. 21, the center of first flow control valve corresponds to zerodegrees on the x-axis. The centerlines of the second, third, and fourthflow control valves occur at an x position equal to 90 degrees, 180degrees and 240 degrees, respectively. For the first run 2001, thevelocity of oil flow at the outer delivery ring 136 increased from theposition of the first flow control valve at x=0 degrees to a maximumflow velocity at x=150 degrees corresponding to the region of the thirdflow control valve. This illustrates a circumferential distribution offlow of the material caused by positioning the first flow control valveoffset from the other flow control valves. When the Z-position of thefirst flow control valve is increased to 1.2 inches in the second run2002, the flow velocity at the outer delivery ring 136 again increasesfrom x=0 to x=150. However, since the difference between the position ofthe first flow control valve and the other flow control valves in thesecond run 2002 is less than the first run 2001, the minimum flowvelocity at x equal to about 25 degrees in the second run 2002 isgreater than the minimum flow velocity for the first run 2001. Referringto FIGS. 22A-22E, a series of photographs of the oil material flowingfrom the distal end 137 of the outer delivery ring 136 furtherillustrate the difference in the flow rates resulting from positioningthe first flow control valve closer to the minimum position than thesecond through fourth flow control valves. As shown in FIGS. 22A-22E,the shape of the meniscus of the oil material (dark region) indicatesthat the flow of the oil material on the left-hand side of FIGS. 22A-22Ecorresponding to the first flow control valve is less than the flow ofthe oil material on the right-hand side of FIGS. 22A-22E, whichcorrespond to the greater flow region created by the second throughfourth flow control valves. This demonstrates that the flow controlvalves may enable control over the circumferential distribution of theflow rate (siding) of material from the cylindrical containers 102 ofthe apparatus 100.

While various embodiments of the apparatus 100 and methods ofcontinuously producing composite glass tubes 200 that include aplurality of glass layers using apparatus 100 have been describedherein, it should be understood that it is contemplated that each ofthese embodiments and techniques may be used separately or inconjunction with one or more embodiments and techniques.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of producing a glass tube comprising:introducing a first molten glass composition to an annular chamberdefined between an inner cylindrical container and an outer cylindricalcontainer, wherein a bottom wall of the outer cylindrical container isspaced apart from the inner cylindrical container to define an annularflow channel; passing the first molten glass composition through theannular flow channel to an outer delivery ring coupled to the bottomwall of the outer cylindrical container and defining a central openingin the bottom wall of the outer cylindrical container; translating atleast one flow control valve disposed in the annular chamber, whereintranslation of the at least one flow control valve relative to the outercylindrical container changes an impedance to flow of the molten glassinto the annular flow channel, thereby changing a thickness of the glasstube; and separating the first molten glass composition from a distalend of the outer delivery ring to form a first molten glass layer of theglass tube.
 2. The method of claim 1, further comprising producing a gasflow proximate to the outer delivery ring.
 3. The method of claim 1,wherein a plurality of flow control valves are disposed in the annularchamber defined between the inner cylindrical container and the outercylindrical container, each of the plurality of flow control valvesbeing independently translatable relative to the outer cylindricalcontainer.
 4. The method of claim 3, further comprising adjusting asiding of the first molten glass layer by translating one or more of theplurality of flow control valves relative to the other of the pluralityof flow control valves to change the circumferential distribution of thefirst molten glass composition flowing through the annular flow channel.5. The method of claim 1 further comprising: introducing a second moltenglass composition to the inner cylindrical container, the innercylindrical container comprising a blow tube disposed within the innercylindrical container; passing the second molten glass compositionthrough an inner annular flow channel defined between the blow tube andthe inner cylindrical container to an inner delivery ring coupled to theinner cylindrical container and defining a central opening of the innercylindrical container; and separating the second molten glasscomposition from the inner delivery ring to produce a second moltenglass layer of the glass tube.
 6. The method of claim 5, furthercomprising contacting the first molten glass layer separated from theouter delivery ring with the second molten glass layer separated fromthe inner delivery ring.
 7. The method of claim 5, further comprisingadjusting a thickness or a siding of the second molten glass layer bytranslating the blow tube vertically or horizontally relative to theinner cylindrical container to change an impedance to flow of the secondmolten glass composition between the blow tube and the inner cylindricalcontainer.
 8. The method of claim 5, wherein the inner cylindricalcontainer comprises an inner flow control valve disposed within theinner cylindrical container and translatable relative to the innercylindrical container, where the method further comprises adjusting athickness or a siding of the second molten glass layer by translatingthe inner flow control valve vertically or horizontally relative to theinner cylindrical container to change an impedance to flow of the secondmolten glass composition from the inner cylindrical container to theinner delivery ring.
 9. The method of claim 5, wherein the first moltenglass composition has a coefficient of thermal expansion (CTE) differentthan the second molten glass composition.
 10. The method of claim 5,further comprising: introducing a third molten glass composition to asecond annular chamber defined between the outer cylindrical containerand a second outer cylindrical container; passing the third molten glasscomposition from the second annular chamber, through a second annularflow channel defined between a bottom wall of the second outercylindrical container and the outer cylindrical container, to a secondouter delivery ring; and separating the third molten glass compositionfrom the second outer delivery ring to produce a third molten glasslayer of the glass tube.
 11. The method of claim 10, further comprisingadjusting an average thickness or a circumferential thickness profile ofthe third molten glass layer by translating at least one of a pluralityof flow control valves disposed in the second annular chamber relativeto the second outer cylindrical container.
 12. A system for producingglass tubing, the system comprising: an apparatus comprising: an innercylindrical container including an inner delivery ring extending from abottom of the inner cylindrical container, the inner delivery ringdefining a central opening in the bottom of the inner cylindricalcontainer; an outer cylindrical container concentrically arranged tosurround the inner cylindrical container and spaced apart from the innercylindrical container to define an annular chamber therebetween, theouter cylindrical container comprising a side wall and a bottom wallextending radially inward from the side wall to an outer delivery ringextending downward from the bottom wall, the outer delivery ringdefining a central opening in the bottom wall of the outer cylindricalcontainer, wherein the bottom wall, the side wall, or both of the outercylindrical container are spaced apart from the inner cylindricalcontainer to define a flow control region and an annular flow channelextending between the outer cylindrical container and the innercylindrical container and from the flow control region to the outerdelivery ring; at least one flow control valve disposed in the annularchamber; at least one positioner operatively coupled to the at least oneflow control valve and operable to translate the at least one flowcontrol valve relative to the outer cylindrical container, the innercylindrical container, or both, wherein translation of the at least oneflow control valve by the positioner is operable to change an impedanceto flow of a molten glass composition through the flow control region;and a blow tube disposed within the inner cylindrical container andoperable to deliver a gas flow proximate the inner delivery ring; asensor disposed downstream of the apparatus, the sensor operable tomeasure at least one dimension of the glass tube produced by theapparatus; and a control system communicatively coupled to the at leastone positioner and to the sensor, the control system comprising aprocessor and one or more memory modules communicatively coupled to theprocessor.
 13. The system of claim 12, further comprising machinereadable instructions stored in the one or more memory modules thatcause the system to perform at least the following when executed by theprocessor: measure a dimension of the glass tube; compare the dimensionof the glass tube to a target dimension of the glass tube; and send acontrol signal to the at least one positioner to change a position theat least one flow control valve based on the comparison of the dimensionof the glass tube to the target dimension, wherein changing the positionof the at least one flow control valve produces a change in thedimension of the glass tube.
 14. The system of claim 12, wherein thesensor is operable to measure at least one of the overall averagethickness of the glass tube, an average thickness of one or more thanone glass layer of the glass tube, a circumferential thickness profileof the glass tube, a circumferential thickness profile of one or morethan one glass layer of the glass tube, an outer diameter of the glasstube, an inner diameter of the glass tube, and combinations thereof. 15.The system of claim 12, wherein the apparatus comprises: a plurality offlow control valves disposed in the annular chamber; and a plurality ofpositioners, each of the plurality of positioners operatively coupled toone of the plurality of flow control valves and operable toindependently translate the one of the plurality of flow control valvesrelative to the outer cylindrical container.
 16. The system of claim 15,further comprising machine readable instructions stored in the one ormore memory modules that cause the system to perform at least thefollowing when executed by the processor: measure a siding of the glasstube; compare the siding of the glass tube to a target siding of theglass tube; and position at least one of the plurality of flow controlvalves relative to the other of the plurality of flow control valves tochange the siding of the glass tube based on the comparison.
 17. Thesystem of claim 12, further comprising a blow tube positioner operableto position the blow tube relative to the inner cylindrical container,wherein the control system is communicatively coupled to the blow tubepositioner.
 18. The system of claim 17, further comprising machinereadable instructions stored in the one or more memory modules thatcause the system to perform at least the following when executed by theprocessor: measure a dimension of the innermost glass layer of the glasstube; compare the dimension of the innermost glass layer of the glasstube to a target dimension of the innermost glass layer; and positionthe blow tube relative to the innermost cylindrical container to changethe dimension of the innermost glass layer of the glass tube based onthe comparison.
 19. The system of claim 18, wherein the dimension is theaverage thickness of the innermost glass layer and the machine readableinstructions stored in the one or more memory modules, when executed bythe processor, cause the system to vertically position the blow tuberelative to the inner cylindrical container.